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Teaching Electricity To Freshman Physical Science Students
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presented by
Jerry Van Horn

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TEACHING ELECTRICITY TO FRESHMEN PHYSICAL
SCIENCE STUDENTS THROUGH CONSTRUCTIVISM

By

Jerry Van Horn

A THESIS

Submitted to
Michigan State University
in partial fulfillment of the requirements
for the degree of

MASTER OF SCIENCE
Division of Science and Mathematics Education

2005

ABSTRACT

TEACHING ELECTRICITY TO FRESHMEN PHYSICAL
SCIENCE STUDENTS THROUGH CONSTRUCTIVISM

By

Jerry Van Horn

The goal of this unit was to teach electricity to freshmen physical science students
using a constructivist approach utilizing a series of laboratories and hands on activities.
The activities were designed to reflect five postulates of constructivist theory: utilize
student’s previous knowledge, require sustained mental effort, create dissatisfaction with
previous knowledge, contain a social component, and apply to the student’s lives. The
hypothesis of this research was that the investigative experiences and constructivist
approach would enhance the students’ conceptual understanding of electricity.

Prior to the unit, the students were given a pre-test that included fifteen short
answer questions that covered information related to the unit. Of the fifty-seven
participants involved in the study, the average score on the pre-test was thirteen point
nine percent. Upon completion of the unit, students were given the same fifteen
questions on a post-test. The average post-test score of the fifty-seven participants
increased to eighty-four point three percent. The data indicate that the unit successfully
reshaped the students’ preexisting knowledge and misconceptions and provided them

with a better conceptual understanding of electricity.

TABLE OF CONTENTS

List of Tables ........................................................................................ v

List of Figures ....................................................................................... vi

Introduction ........................................................................................... 1

Scientific Background ...................................................................... 5

Demographics .............................................................................. 10

Implementation of the Unit ........................................................................ 12

Summary of Activities ..................................................................... 14

Evaluation

Quantitative Data ........................................................................... 23

Qualitative Data ............................................................................. 30

Discussion ................................................................................................. 33

Appendices A: Electricity Unit Student Work .

A-l :
A-2:
A-3 :
A-4:
A-S:
A-6:
A-7:
A-8:
A-9:

A-lO:
A-ll:
A-12:
A-13:
A-14:
A-15:
A-16:
A-17:
A-18:

Appendices B: Electricity Unit Teacher Resources

Electrostatics Mini-Labs .........................................................
Charged Grains Lab ...............................................................

Electroscope Lab ..................................................................

.36

.37
.40

43

Electrophorus and Leyden Jar Lab .............................................. 46
Flowing Water Mini-Lab ......................................................... 49

Current Lab ........................................................................

.50

Resistance Lab ..................................................................... 53
Cells in Series and Parallel Lab56

Circuits in Series and Parallel Lab ..

....59

Ohm’s Law Lab........... 62

Ohm’s Law with Series CircuitsLab
Ohm’s Law with Parallel Circuits Lab

..65
..69

Fuses Lab ........................................................................... 72

Home Wiring Lab

.75

Cost ofElectricity Act1v1ty77

Electricity Unit Study Guide .....................................................
Electricity Pre and Post-Test
Electricity Multiple Choice Test

iii

78

.83
.85

.91

B-l :
B-2:
3-3:
8-4:
8-5:
B—6:
B-7:
B-8:
B-9:

B-10:
8-11:
8-12:
B-13:
8-14:
3-15:
B-16:
B-17:
B-18:

References. . .

Teacher’s Guide for Electrostatics Mini-Labs .................................. 92

Teacher’s Guide for Charged Grains Lab ...................................... 93

Teacher’s Guide for Electroscope Lab .......................................... 94
Teacher’s Guide for Electrophorus and Leyden Jar Lab ...................... 95
Teacher’s Guide for Flowing Water Mini-Lab ................................. 96
Teacher’s Guide for Current Lab ................................................ 97
Teacher’s Guide for Resistance Lab ............................................. 98
Teacher’s Guide for Cells in Series and Parallel Lab ........................ 100
Teacher’s Guide for Circuits in Series and Parallel Lab .................... 103

Teacher’s Guide for Ohm’s Law Lab .......................................... 105
Teacher’s Guide for Ohm’s Law with Series Circuits Lab ................. 109
Teacher’s Guide for Ohm’s Law with Parallel Circuits Lab .................... 111

Teacher’s Guide for Fuses Lab ................................................. 114
Teacher’s Guide for Home Wiring Lab ........................................ 116
Teacher’s Guide for Cost of Electricity Activity ............................. 117
Teacher’s Guide for Electricity Unit Study Guide ........................... 118
Teacher’s Guide for Electricity Pre and Post-Test ........................... 121

Teacher’s Guide for Electricity Multiple Choice Test ....................... 124
............................................................................................ 125

iv

LIST OF TABLES

Table 1: Average Pre-Test and Post-Test Scores by Class Period ........................... 23

LIST OF FIGURES

Figure l: Flowchart for electrostatic portion of unit .......................................... 15
Figure 2: Flowchart for electrical current portion of unit .................................... 18
Figure 3: Fourth Hour Average Scores on the Three Point Test Questions ............... 24
Figure 4: Fifth Hour Average Scores on the Three Point Test Questions .................. 25
Figure 5: Sixth Hour Average Scores on the Three Point Test Questions ................. 25
Figure 6: Fourth Hour Average Scores on the Two Point Questions ....................... 27
Figure 7: Fifth Hour Average Scores on the Two Point Questions ......................... 28
Figure 8: Sixth Hour Average Scores on the Two Point Questions ......................... 28

vi

Introduction

The Fowlerville science staff analyzed the science curriculmn and made
significant changes to the Physical Science curriculum during the 2002 — 2003 school
year. Analysis of the High School Proficiency Test showed that Fowlerville students
were scoring low in a number of physics related objectives. Up to this point, the semester
long ninth grade physical science class was primarily chemistry based. Topics such as
mechanics, heat, electricity, magnetism, and nuclear physics were not covered. The
chemistry objectives taught, however, were reinforced in the students’ chemistry class or
a junior level integrated science class prior to the eleventh grade proficiency test. Since
the students were not introduced to the required physics objectives, the staff decided that
the physical science class would shifi from a chemistry-based curriculum to a physics-
based curriculum in the fall of 2003.

Since my research was being conducted during the summer of 2003, I needed to
choose a topic that I had not taught before. I decided to work on a topic generally
emphasized on proficiency tests as well as a topic in which I felt relatively weak:
electricity. Since I did not take physics in high school, the extent of my electrical
knowledge came from a ninth grade Physical Science class, a Physics 11 college class at
Central Michigan University, and a Physics for Teachers lab course at Michigan State
University. I remember little from my high school class and was thoroughly perplexed
by my college class. The professor moved very rapidly and presented material from a
theoretical perspective. Consequently, I memorized enough to get by, but had a very
weak conceptual understanding. It was not until I had completed the Physics for
Teachers laboratory course at Michigan State University that I had gained a strong

foundation of electricity. There I completed a lab based electricity curriculum, called

CASTLE (capacitor aided system for teaching and learning electricity), that provided me
with an excellent fi'amework for thinking about electricity.

With this foundation, I set out to design a unit that could be presented to my
students through a series of experiments, activities, and demonstrations that would make
a difficult concept engaging, understandable, and relevant. In order to achieve this, I
decided to design the unit around constructivist theory. Constructivism has become an
integral part of current education reform and is supported by the National Science
Education Standards and Project 2061 (Haney, Lumpe, Czemiak, 2003). My hypothesis
for this research is that teaching the unit using a constructivist approach will successfully
improve the students conceptual understanding of electricity.

Constructivists assume that knowledge is actively constructed in the mind of the
learner. One constructivist theorist, Thomas W. Shiland, believes that constructivist
theory can be explained through five basic postulates (1999). First, learning requires
sustained mental effort. Learners do not incorporate ideas into a meaningful mental
framework by having material simply presented to them (Driver, 1988). Rather,
learners need to grapple with new information in order to gain a foundation that makes
sense to the learner. As a result, constructivists feel that the behaviorist approach to
learning is inadequate. Simply presenting material to students and asking them to
memorize and recite that material back does not result in learning. In fact, numerous
studies have shown that most college students hang on to grand misconceptions even
after successfully passing a course (Lorsbach et a1. 1995). Therefore, while it may be
possible to memorize factual material and successfully relay that information back, it is
apparent that without deeper thinking, naive ideas remain firmly implanted in the mind of

the learner.

A second basic postulate of constructivist theory is that students’ prior knowledge
is important and relevant to the learning process (Jofili, Geraldo, & Watts 1999). When
students enter classrooms, they come to class with a host of explanations for how the
world around them works. Therefore, when students are offered new insights into a
topic, they can deal with it in one of four ways: delete their preexisting knowledge,
modify their preexisting knowledge so that it meshes with the new information, modify
the new information so that it fits with their preexisting knowledge, or reject the new
information altogether (Sewell, 2002). Since little thought is required to simply ignore
new information altogether, many students resort to it. Consequently, constructivists
believe that it is the teacher’s job to identify misconceptions that are widely held by the
students and to address those misconceptions. Instead of dismissing the misconceptions
as incorrect, the teacher should provide students with opportunities to explore other
possibilities that allow students to determine the flaws in their initial fi'amework while
developing new ideas that are more intellectually sound (Windschitl, 1999). Once this
has been accomplished, constructivists believe that a deeper level of understanding is
attained while previous misconceptions are replaced.

Shiland’s third postulate of constructivist theory is that meaningful learning
occurs when learners are dissatisfied with their present knowledge. This means that if
learners are able to correctly hypothesize how an unknown situation will turn out, a
restructuring of information will not occur (Saunders, 1992). Therefore, a correct
solution to a problem may deepen a leamer’s level of understanding about a topic, but the
learner has not had to reshape his thinking. It is when an expected outcome does not
occur that a learner needs to reevaluate his existing knowledge and restructure it so that it

encompasses the new information. This allows the learner to dismiss previous

misconceptions and provides him with a stronger foundation than he previously had.

A fourth postulate to constructivist theory is that learning has a social component.
When discussing new information that has been assimilated, learners test the fit of that
information into their new fiamework of understanding (Lorsbach & Tobin 1993). If
they have truly learned something, they should be able to express that information to
others in a clear and concise way, thus deepening their understanding. Likewise,
individuals listening to someone else can learn meaningfully by constantly assessing and
questioning the material being presented so that it fits with their preexisting knowledge
(Lord, 1998).

Shiland’s final postulate of constructivist theory is that learning needs application.
In order to maximize learning, students need to be exposed to applications that
demonstrate the value of the new concept. Therefore, to get learners to buy-in to the
importance of a topic, they need to see how the topic relates to them personally.
Relevance plays a critical role in learning. Without it, learners fail to see the importance
of a topic. As a result, thought about the topic is minimized and meaningful learning is
not attained. By relating concepts to students’ lives, their interest level is raised and they
are provided with a context for thinking about the new topic.

In addition to these five postulates, I believe that the constructivist teacher needs
to provide students with opportunities to learn material in different ways. With the
traditional behaviorist approach, students are presented with information from the teacher
and the textbook and expected to learn the material. However, there are multiple ways
that individuals learn. A traditional approach of teaching utilizes primarily analytical and
verbal learning. According to Gardner, however, there are nine distinct categories of

learners (Gardner, 2000). Therefore, to provide students with an optimal chance to learn,

they must engage in activities and materials that suit them best. These activities include
those that are suited not only to analytic and verbal learners, but also to visual, spatial,
kinesthetic, and interpersonal learners as well.

Scientific Background

Around 600 BC, a Greek philosopher named Thales of Miletus discovered that
amber would attract bits of dust and small particles after it had been rubbed with fur.
Unknowingly, he had discovered electrostatics. Electrostatics is the study of electrically
charged objects. An object becomes electrically charged when it has an excess of either
positive or negative charge.

The positive and negative charges responsible for Thale’s discovery come fi'om
small particles called atoms. Atoms are the building block of all matter and consist of
three smaller particles known as protons, neutrons, and electrons. Each atom contains a
positively charged center called the nucleus. The nucleus contains both positively
charged protons and uncharged neutrons, and it is held together very tightly.
Surrounding the nucleus is the electron cloud which contains negatively charged
electrons. The electrons are not held as tightly as the protons and neutrons are. Although
protons are more massive than electrons, the two particles carry the same quantity of
charge. Since the number of protons is typically the same as the number of electrons,
atoms are generally neutral. Therefore, even though charges exist within atoms, they do
not act as charged bodies because the amount of positive and negative charge offset one
another.

When two bodies are brought together, however, charge can be transferred from
one object to another. This occurs because objects have different affinities for electrons.

Some objects, like amber, have strong affinities for electrons. This means that when an

object like fur is rubbed against amber, some of the loose outer electrons in atoms making
up the fur are “scraped” off onto the amber. Once this happens, the amber has more
electrons than it does protons. As a result, the amber becomes negatively charged. Fur,
on the other hand, loses negatively charged electrons. Therefore, there are more protons
than there are electrons making the fur positively charged. It is important to note that
electrons have not been created or destroyed during this process. Instead, electrons were
simply transferred from the fur to the amber. The total amount of charge has been
conserved throughout this process.

If the firr and the amber are brought near one another after they have been
charged, the two objects will attract. This occurs because objects that have opposite
electrical charges exert an attractive force on one another. If two objects with like
charges are brought near one another, the two objects will repel because objects with like
electrical charges exert a repulsive force on one another.

The size of the force that is exerted on two point charges depends on two factors:
the quantity of charge on the two particles and distance the particles are separated. This

relationship was discovered by Charles Coulomb and can be expressed as

F=kgl
dig

where k represents the proportionality constant, ql and q; represent the quantity of charge
in coulombs on the particles, and d is the distance the particles are separated. The
coulomb, abbreviated C, is the amount of charge contained in 6.25 x 1018 electrons or
protons. This equation shows that if the distance between two particles remains constant,
the force between them will increase if the charge on either of the particles increases. It
also shows that if the charges on the particles remain constant, the force between them

will increase if the particles are moved closer together.

6

Interestingly, a charged object can also exert a force on an uncharged object
located nearby. For example, when the amber is rubbed with fur it becomes negatively
charged. When the amber is placed near dust, the dust will accelerate from its stagnant
position toward the amber until the two are sticking together. This occurs because the
amber induces a charge in the neutral dust. The centers of positive charge within the dust
are shifted so that they migrate toward the amber. While the dust is still neutral overall,
the charges have been redistributed such that the amber and dust are attracted to one
another.

Another type of electricity was discovered accidentally by Luigi Galvani in 1780
as he was dissecting a frog. During the dissection, Galvani was able to successfully
move a charge through a frog’s leg causing it to twitch. Unwittingly, Galvani developed
a technique whereby a sustained flow of electric charge was possible. This accident led
to the discovery of electrical current.

While electrostatics addresses objects that have a net charge, electrical current
deals with the flow of charge. Oftentimes, this flow occurs in an uncharged object such
as a copper wire. The flow of charge is known as electrical current and is defined as the
rate at which charge flows through some substance. Electrical current is expressed in
amperes, abbreviated A. One ampere is equal to one coulomb of charge moving through
a substance in one second. This is roughly the amount of current that passes through a
one hundred watt light bulb connected to a household circuit in the United States every
second.

One thing that determines the amount of current that flows through a circuit is the
voltage that is applied across the circuit. One can think of voltage as electrical pressure.

Just like pressure is needed to get water to flow, pressure is needed to get electric charges

to flow. The greater the amount of pressure, the greater the flow of charge will be.
Therefore, in order to get current to flow through a circuit, a voltage difference must exist
across the ends of the circuit. Without a difference in voltage, a pressure gradient does
not exist and charge will not flow. The greater the pressure gradient is, however, the
greater the current will be. Voltage, also known as potential difference, is measured in
volts, abbreviated V.

A second factor that determines how much current will flow through a circuit is
resistance. As current flows through a circuit, individual charge carriers encounter
fiiction as they move. Since fiiction always acts in a direction that is opposite to the
motion of an object, the friction the charge carriers encounter acts to slow them down. In
an electric circuit, this fiiction is known as resistance. A number of factors affect the
overall resistance in a circuit. These factors include the length of the resistor, the
diameter of the resistor, the temperature of the resistor, and the material out of which the
resistor is made. If a circuit contains a single resistor and the quantity of that resistor is
increased while the voltage remains constant, the amount of current flowing through the
circuit will decrease.

The relationship between current, voltage, and resistance was first described by
Georg Ohm in the early 1800’s. He determined that the current flowing through a circuit
was directly proportional to the voltage applied across the circuit and inversely
proportional to the resistance of the circuit. Ohm’s Law, therefore, can be expressed as:

I=V

R
where I stands for current, V for voltage, and R for resistance. Consequently, to

maximize current flow through a circuit with one resistor, the voltage applied across the

circuit should be maximized while the overall amount of resistance within the circuit
should be minimized.

Current is generally carried through circuits, pathways along which charge flows.
In order to get a sustained current flow, the circuit must be free of gaps and allow charge
to be carried. These types of circuits are called closed circuits. In order to stop current
from flowing, the pathway must be broken. This type of circuit is an open circuit.
Generally, switches are employed in a circuit and act to open and close the circuit as
needed. Circuits can be connected together in one of two primary ways: series or
parallel.

Ohm’s law can be applied to series and parallel circuits to help one understand
why these circuits function differently. A series circuit contains a single pathway for
charge to flow through. Since there is only one pathway, the current at each spot in a
series circuit has to be the same. To determine how much current there is in a series
circuit one needs to determine the sum of the resistances in the circuit. The total current
flowing though the circuit is determined by dividing the total voltage applied across the
circuit by the sum of the individual resistors in the circuit. This has some interesting
ramifications. If the circuit contains resistors that have different amounts of resistance, it
follows that the voltage drops across the different resistors must be different. Therefore,
a resistor with a large amount of resistance requires a large voltage drop across it. This
makes sense if one realizes that the current needs to be the same at each location within
the circuit. A greater electrical pressure is required to push a certain amount of current
through a high resistance. If one were to look at the voltage drop across each individual
resistor, the sum of those voltage drops would be equal to the voltage drop applied across

the entire circuit.

A parallel circuit, on the other hand, contains multiple pathways through which
current can travel. Since there are multiple pathways for current to travel through, the
amount of current in one branch may be different from the amount of current in a
different branch. Since each branch connects directly to the power source, the voltage
drop across each branch is equal to the voltage supplied by the power source. Therefore,
a branch that has less resistance will have a larger current passing through it. In order to
determine the total amount of current running through a parallel circuit, one would need
to calculate the current running through each branch of the circuit. The sum of these
currents is equal to the total amount of current in the circuit. An interesting ramification
of adding additional branches to a parallel circuit is that it serves to reduce the overall
amount of resistance within the circuit. As the overall amount of resistance decreases,
the amount of current flowing through the circuit increases. This can be problematic
because larger currents mean more heat is produced. This raises the risk of an electrical
fire. As a result, fuses and circuit breakers are typically wired into parallel circuits for
safety purposes.

Demographics

This study was conducted with fi'eshman enrolled in three Physical Science
classes at Fowlerville Jr. High School. Fowlerville is a small, rural village located
approximately thirty miles east of Lansing. Ethnically, it is a relatively non-diverse
community of 15,757 individuals. Caucasians comprise over ninety-five percent of the
population. Economically, on the other hand, the community is quite diverse. The
median household income is $60,337 which exceeds the state average by $12,041. While
the median household income is greater than the state average, the number of adults in

the community who possess a bachelor’s degree is nearly ten percent less than the state

10

average. This data leads one to believe that there is an affluent group of well educated
individuals within the district that raises the overall median household income. At the
same time, there is a group that is not as well educated that make much less money.
These numbers help explain the economic disparity I see between students on a daily
basis.

F owlerville Jr. High has approximately 830 students in grades seven, eight, and
nine. At the beginning of this study, 277 of those students were in ninth grade, of which I
taught eighty-seven. Fifty-seven of these students agreed to participate in the study. Of
the fifty-seven students, twenty-nine were female; twenty-eight were male; fifty-six were
Caucasian and one was Asian.

Physical Science is one of three credits needed in science to graduate from
Fowlerville. Consequently, all incoming fi'eshman are required to take the course unless
they are able to successfirlly test out of the class. We do not offer an “advanced” physical
science course; therefore, a wide range of ability levels are present in each class. For
instance, some students in my science class also take a low-level algebra course while
other students in my class are taking geometry and algebra-II courses. This wide
disparity of intelligence and motivation has made teaching the course so that all students

receive a meaningful education difficult.

11

Implementation
Constructivist theory states that students’ prior knowledge is important and
relevant to the learning process. Therefore, before I designed the unit, I set out to
determine common misconceptions about electricity that are widely held. I know from
personal experience that these misconceptions can be detrimental to the learning process.
These misconceptions must be addressed so that students can maximize their learning
potential. Below are some widely held misconceptions about electricity (Science
Education Center, 2002), (Hewitt, Suchocki, and Hewitt 2003).
1. Static electricity is electricity that is static — not moving.
2. Static electricity is a build-up of electrons — it has nothing to do with protons.
3. Electrical charges occur in some materials but not in others.
4. Current electricity is the opposite of static electricity.
5. A current carrying wire is electrically charged.
6. Electric current flows out of a battery, not through it.
7. Electric current is the flow of electrons - nothing else.
8. Electric current moves at the speed of light.
9. Voltage and current are two words for the same thing.
10. Voltage flows through a circuit.
11. In series circuits, the amount of current varies in devices of different electrical
resistance.
12. In a parallel circuit, the equivalent resistance of the circuit increases with the addition
of more resistors.
I looked for labs and activities that addressed these misconceptions. It was my

goal to provide students with opportunities to discover inadequacies in their own thinking

12

so that they could restructure their thoughts. According to constructivist theory, this is
much more powerful than simply telling students that their current thoughts are wrong
and telling them how they should think. In addition to looking for labs that addressed
misconceptions, I searched for activities that incorporated the five basic postulates of
constructivist theory mentioned earlier. The labs and activities should require sustained
mental activity, utilize and create dissatisfaction with previous knowledge, contain a
social component, and be applicable to the students’ lives.

A final item that I considered before designing my unit was the type of equipment
to use. Oftentirnes, teachers use the best laboratory equipment available when studying a
topic. Unfortunately, students don’t always make the necessary connections when they
are using sophisticated equipment. Consequently, I decided to use common everyday
materials to introduce my unit. More sophisticated equipment was introduced after
students had a firm foundation with the basic concepts of electrostatics and current

electricity.

l3

Summary of Activities

The electricity unit was introduced during the twelfth week of the second
semester and was completed over the course of five weeks. Prior to the start of the unit,
students were given a Pre- Test (A-l 7) that contained fifteen questions based on the
objectives of the unit. Upon completion of the pre-test, students were introduced to the
electricity unit which was broken down into two basic categories: electrostatics and
electrical current. Throughout the unit, students were engaged in numerous labs and
activities that can be found in appendix A. The manner in which the labs were assessed
can be found in appendix B — the teacher section of the unit.

The electrostatics portion of the unit was covered in the first week and a half.
Four labs and a munber of demonstrations involving a Van de Graaff generator were
performed during this part of the unit as shown in Figure One on page fifteen. These
activities addressed the three electrostatics' objectives:

Objective 1: Describe how electric charges are transferred and explain why electric
discharges occur.

Objective 2: Analyze factors that affect the strength and direction of electric forces.
Objective 3: Determine the polarity of an unknown charge using an electroscope.

The labs and assignments found in appendix A are arranged in the same order
that they were distributed to the students. The electrostatics portion of the unit began
with an electrostatics mini-lab activity (A-1) and a charged grains lab (A-2). Both
activities were designed to engage the students and draw them into the study of
electrostatics by having them perform various “magical” tricks using common everyday
materials. Many students were mesmerized by the fact that they could charge themselves

and cause a pencil to move simply by moving their finger back and forth near the tip of a

14

 

Electrostatic
Portion of
Unit

E lectroatatica
Mini-Labs
Charged
Grains Lab

Van de G raaf
Generator
Demos

Electroscope
Lab

Electrophorus I

Leyden Jar Lab

Figure l: Flowchart for electrostatic portion of unit

   
      
    
   

  

 

 

 

 

 

 

 

pencil. After completing the two labs, students had been introduced to the idea that
charge can be transferred to an object through fiiction, conduction, and induction.
Furthermore, they determined that opposite electrical charges attract while like electrical
charges repel. In addition, they concluded that the electrical force between two objects
depends on the amount of charge on the objects and how far the objects are separated
from one another.

After completing these labs, the students were introduced to the Van de Graaff
generator. Since it was my first time teaching the unit, I was unsure of what to expect. I
quickly learned that any interest I had elicited with the first two labs paled in comparison
to the enthusiasm brought about by the generator. Students were very excited to take part

in the demonstrations that reinforced the topics covered in the first two labs. The two

15

demonstrations that brought about the most interest were the hair raising demonstrations
and the large sparks created by the discharge of the generator.

Following the excitement of the Van de Graaff generator, students performed an
electroscope lab (A-3). The students used hand-made electroscopes to explore
electrostatic charges through both conduction and induction. Students also detenrrined
how to use the electroscope to identify the polarity of an unknown charge.

After completing the electroscope lab, I showed the students that a metal
enclosure, known as a Faraday cage, located around an electroscope prevented the
electroscope from becoming charged. The students saw that an electroscope placed
inside a metal pot and covered with a metal strainer could not be charged. Even when a
Van de Graaff generator was placed near the electroscope, it failed to become charged.
They discovered that an electrostatic charge placed on a metal enclosure remains on the
outside surface of the container. Many of the students found it interesting that this was
the reason why it was safe to be inside a car during a thunderstorm. Many were under the
false impression that a car was safe because of the of the car’s insulated tires.

The final activity of the electrostatics portion of the unit was the Electrophorus
and Leyden Jar lab (A-4). During this activity, students used an electrophorus capable of
producing a large number of successive electrostatic charges. These charges were
transferred to an aluminum pie pan and in turn transferred to a device called a Leyden
Jar. The Leyden Jar stored large amounts of charge until the students were ready to
discharge it. The Leyden Jar was a precursor to today’s capacitor, a device used in
electrical circuits.

The Leyden jar lab provided a nice transition from the subject of electrostatics to

electrical current. We discussed the fact that large amounts of charge could be stored and

16

discharged through objects, but that a sustained flow of charge was not possible with this
device. With that, we shifted our focus from electrostatics to current electricity. This
portion of the unit was completed in three and a half weeks. Ten labs and a project were
performed during this part of the unit as shown in Figure Two on page eighteen. The
activities were completed to address ten electrical current objectives:
Objective 1: Distinguish a conductor from an insulator.
Objective 2: Describe the conditions necessary for electric current to flow.
Objective 3: Describe the factors that affect resistance.
Objective 4: Relate the current in a circuit to the resistance of the circuit and the voltage
across it using Ohm’s Law.
Objective 5: Analyze the differences between cells connected in series and in parallel.
Objective 6: Construct and analyze circuits using circuit diagrams.
Objective 7: Analyze the differences between circuits connected in series and in
parallel.
Objective 8: Describe devices and procedures for maintaining electrical safety.
Objective 9: Determine the cost required to rrm various electrical devices based on
current electrical costs.
Objective 10: Connect a household circuit containing two outlets, a switch, and a light
fixture.

The electrical current portion of the unit began with the Water Analogy activity
(A-S). Two bottles were attached by a piece of tubing that connected the bottom of the
bottles together. When the tubing was clamped and water was placed into one bottle, the
water stayed in that bottle. As soon as the students removed the clamp, water began

immediately pouring through the tube into the second bottle. The flow continued until

17

 

   
      

Current Lab
Resistance
Lab

Cells in
Series and
Parallel Lab

     
   
  

  
      
      
 
   
 
  

Circuits in
Series and
Parallel

    
 

 
  

Ohm's Law
with Series
Circuits Lab

Ohm's Law
with Parallel
Circuits Lab

  
 
   

Household
Wiring Lab

  

Fuses Lab

 

 

 

 

Figure 2: Flowchart for electrical current portion of uni?

 

18

the water was at the same level in both bottles. After completing the activity, we
discussed the similarities between the flow of water and the flow of electricity. This was
an invaluable activity to begin with because it provided the students with a framework for
thinking about current and voltage.

After completing the Water Analogy activity, students began the Current Lab (A-
6). During this lab, students connected copper and zinc electrodes in various
arrangements and in various media to determine when current would flow. In order to
measure the flow of current, students used homemade galvanoscopes that consisted of
many turns of wire placed around a compass. Current flowing through the compass
causes the needle to deflect. The stronger the current was that flowed through the circuit,
the greater the deflection of the compass needle. After completing the lab, students
realized that they had created voltaic cells that worked when two different electrodes
were separated by an electrolyte. They also realized that the amount of current was
greater when more than one cell was connected together.

Once the students had been introduced to electrical current, they explored how
that current could be affected by resistance. During the resistance lab (A-7), students
looked at how resistor length and diameter affected the amount of current flowing
through a circuit. In order to look at resistor length, students used a homemade rheostat
made out of a shaved pencil. Students hooked a circuit up that included some batteries, a
light bulb, and the shaved pencil. They determined that the shorter the pencil lead
resistor was, the brighter the light bulb glowed. Consequently, they determined that
shorter resistors provided less resistance than did longer ones.

Next, the students looked at resistor diameter and its effect on resistance. Since

Play-dob conducts electricity, they made different diameter “wires” out of the Play-Dob

l9

and inserted these Play-dob cylinders into a circuit. Using multimeters, students
measured the current running through the circuit and the voltage across the Play-doh
resistor. They then calculated the amount of resistance to determine that as the diameter
increased, the total amount of resistance decreased.

After exploring the basics of current, voltage, and resistance, the students began
investigating circuits in more detail. In the Cells in Series and Parallel lab (A-8),
students examined how connecting cells in series and parallel affected a circuit. During
the lab, students used zinc and copper electrodes dipped in a salt water solution. They
connected the cells together in both series and in parallel and measured the voltage across
the cells. Once complete, the students realized that the voltage across cells in parallel
was identical to the voltage across a single cell while the voltage across cells in series
was equal to the sum of the voltages across each individual cell.

The next lab that the students encountered was the Circuits in Series and Parallel
lab (A-9). While the information in this activity was primarily a review for the students,
it was very important that they knew how to connect circuits together in series and
parallel for some more complex labs that were forthcoming. In the lab, students explored
both series and parallel circuits and were reminded about their differences.

Following this lab, the students completed three successive labs related to Ohm’s
Law. During the first lab, the Ohm ’s Law lab (A-lO), students investigated the
relationship between current, voltage, and resistance. At this point, they already knew
that more voltage meant more current and more resistance meant less current. They did
not, however, know exactly how these quantities related to one another. Consequently,
the students completed a two part lab where either the voltage or the resistance of a

simple circuit was held constant while the other value changed. After completing the lab

20

and graphing the data, students realized that current was directly proportional to voltage
and inversely proportional to resistance.

Next, students completed the Ohm ’s Law with Series Circuits lab (A-l 1) and the
Ohm ’s Law with Parallel Circuits lab (A-12). During these two labs students
investigated series circuits and parallel circuits and learned how Ohm’s Law can be
applied to each type of circuit. For instance, students learned that as more resistors are
added in series, the total amount of resistance in the circuit increases. As more resistors
are added in parallel, however, the total amount of resistance decreases. These ideas can
be major stumbling blocks for students so we spent considerable time on these two labs.

Once the students had been introduced to parallel circuits and resistance, students
recognized that adding additional resistors in parallel posed a real safety risk. A decrease
in resistance means a corresponding increase in current. In turn, this means an increase
in the amount of heat generated and a real possibility of an electrical fire. Consequently,
we performed the Fuses Lab (A-l 3) to illustrate how circuit breakers and fuses are used
in modern day electrical circuits. Students discovered that fuses and circuit breakers help
protect circuits against overloads and short circuits.

After discussing fuses and circuit breakers and how they are incorporated into
household circuits, we began our last lab: the Home Wiring Lab (A-14). In this
lab, students were shown how outlets, switches, and light fixtures are connected with a
PowerPoint presentation. They were required to take notes so that they would be able to
connect two outlets, a switch, and a light fixture.

The final assignment in the electricity unit was the Cost of Electricity activity (A-
15). After learning about how electricity works I wanted to make sure that the students

had an understanding of how much it cost to use various electrical devices. Each student

21

picked out three devices that he or she felt was important and calculated the amount of
money required to use those devices for a month.

Upon completion of the unit, students were given the Electricity Unit Study Guide
(A-16). After completing and reviewing the study guide, students took the fifteen
question short answer Post- Test (A- l 7). This test was identical to the pre-test that
students took at the beginning of the unit. In addition, the students were given a 50

question Electricity Multiple Choice Test (A-18).

22

Evaluation
Quantitative Data

At the beginning of the electricity unit, the students were given a 15 question
short answer pre-test. The test, appendix A-l 7, was comprised of ten two point questions
and five three point questions that covered the unit’s objectives. The rubric that was used
to grade these tests is found in appendix B-1 7. Upon completion of the unit, the students
were given the same 15 question test. Average scores on the pre-test and post-test for my

fourth, fifth, and sixth hours are shown in Table l.

 

Fourth Hour Fifth Hour Sixth Hour

 

Pre-Test Post-Test Pre-Test Post-Test Pre-Test Post-Test

 

 

14.0% 80.7% 14.4% 85.1% 13.3% 87.1%

 

 

 

 

 

 

 

 

Table 1: Average Pre-Test and Post-Test Scores by Class Period

 

 

 

The results show a dramatic increase in correct responses fi'om the pro-test to the
post test. Fourth hour scores increased by 66.7%, fifth hour scores increased by 70.7%,
and sixth hour scores increased by 73.8%. The dramatic increase in scores can be
attributed to three factors. First, students knew that the pre-test was going to be used to
provide baseline data for my thesis. They knew that it would not be counted as a grade,
so some individuals may not have put forth their best effort. Second, the pre-test was
given with approximately thirty nrinutes left in class on the first day of the unit.
Therefore, students did not have the entire sixty minute class period to work on the test.
Questions that were not finished in class were to be taken home and completed as
homework. Consequently, some students did not complete all of the questions causing

the average score to be less than it otherwise might have been. Third, and most

23

importantly, students really did have a limited electrical knowledge and genuinely
struggled with the pre-test.

After completing the unit, however, students apparently had gained a firm
conceptual foundation and were able to answer most of the questions to a high degree of
competency. The pre-test and post-test were broken down by question number and
analyzed. Figures 3, 4, and 5 represent the average score students in different hours

received on each of the three point test questions.

 

; I Pre-Test
l I Post-Test

Score Out of Three

 

 

 

Question Number

 

Figure 3: Fourth Hour Average Scores on the Three Point Test Questions (11 = 20)

 

 

 

24

 

I Pre-Test
I Post-Test

Score Out of Three

 

 

 

Question Number

 

 

Figure 4: Fifth Hour Average Scores on the Three Point Test Questions (n = 20)

 

 

 

2.5 . [

  
 

N
l

I Pre-Test
I Post-Test

Score Out of Three

0.5

 

 

Question Number

 

 

Figure 5: Sixth Hour Average Scores on the Three Point Test Questions (11 = 17)

 

 

25

Figures 3, 4, and 5 show a dramatic increase in all of the three point short answer
questions. The average score for the three hours combined ranged from a high of 96% on
question number seven to a low of 74% on question nine. The higher post-test scores for
question number seven are due to the fact that the question was a recall problem.
Students needed to recall the units that are used to measure current, voltage, and
resistance. Since we had worked extensively in labs with current, voltage, and resistance,
this proved to be an easy question for most students. In fact, all of the students in my
fourth and sixth hour classes answered this question correctly.

The two questions on which students scored below an 80% were question
numbers three and nine. It was disturbing that the average score for question number
three was a 77%. In each of the three hours, this question received the highest pre-test
scores. However, on the post-test, it proved to be the second most diffith three point
question. The question asked the students to differentiate an insulator from a conductor
and to give an example of each. While we discussed this concept briefly in class, we did
not perform a specific lab on conductors and insulators. I knew the students had been
introduced to this concept in seventh grade. I felt that I could briefly review the subject
assuming the students already knew the material. Unfortunately, only 25% of the
students were able to answer the question on the pre-test correctly. Therefore, my
assumption about their prior knowledge was incorrect. Furthermore, it shows that
learning by discussing a topic is not as effective as a hands-on activity for most students.

The question which received the lowest marks on the post-test was question
number nine. This question asked the students how voltage and resistance affected the
current in a circuit. It went on to ask what would happen to the amount of current if the

voltage was doubled and what would happen to the current if the resistance was doubled.

26

The reason why this question scored the lowest was because students did not specifically
explain that the current would double if the voltage was doubled and that the current
would be halved if the resistance was doubled. Since they were not specific, they did not
earn the total number of points. This is unfortunate because most students understood the
relationship based on my classroom observations.

Figures 6, 7, and 8 represent the average score students earned in different hours
on each of the two point test questions. The average scores on the post-test for the three
hours ranged from a high of 100% on question number eleven to a low of 64% on

question number fourteen.

7 I Pre-Test I

I Pest-Test r

Score Out of Two

 

 

 

 

24516181112131415
QuestionNumber

 

Figure 6: Fourth Hour Average Scores on the Two Point Questions (n = 20)

 

 

 

27

 

l"

l I Pre-Test
l I Post-Test

Score Out of Two

 

 

 

 

2 4 5 6 8 1 1 12 13 14 15
Question Number

 

 

 

Figure 7: Fifth Hour Average Scores on the Two Point Questions (11 = 20)

 

 

I PrE-Test
I Post-Tog

Score Out of Two

 

 

2 4 5 6 8 11 12 13 14 15
QuestionNumber

 

Figure 8: Sixth Hour Average Scores on the Two Point Questions (n=l7)

 

 

28

Of the two point questions, only questions fourteen and fifteen had fewer than
80% of the students answering the questions correctly. These two questions were
difficult because they addressed the intricacies of series and parallel circuits. Question
number fourteen proved to be the hardest question on the test. It asked students to
describe the relationship between the voltage of a battery and the voltage drop across
each resistor in a series circuit and in a parallel circuit. While two of the labs that we
completed in class directly illustrated what they needed to answer this question, it is
apparent that the students did not have the cognitive fiamework to answer this question as
well as some others. It should be noted, though, that 64% of the students in the study did
answer this difficult question accurately. Question number fifteen was similar to number
fourteen. Instead of asking about voltage, question fifteen dealt with the amount of
current at different places in a series circuit, including the battery. One of the
misconceptions mentioned earlier was that current flows out of a battery, not through it.
Unfortunately, this misconception was still held by some of the students at the end of the
unit. On a positive note, 75% of the students did answer this question correctly.

After breaking the pre and post-test down by number, a paired t-Test was run on
both the two point and the three point questions to verify that there was a statistical
difference between the pre-test and the post-test that could be attributed to the unit. After
running the test on the two point questions, the probability that the pre-test and post-test
results were statistically different from one another was greater than 99.99%. Likewise,
the paired student t-Test run on the three point test questions showed a greater than

99.99% chance that the two data sets were statistically different.

29

Qualitative Data

Throughout the electricity unit I repeatedly heard students comment on how much
they were enjoying it. I often heard comments on how the labs were more fun than either
lectures or worksheets. Occasionally, I overheard students discussing the usefulness of
the labs or saw eyes light up with wonder and excitement. I also noticed that many
students who had previously not put forth much effort were actively involved with the
labs. Sometimes, these students even took the lead and would tell others what to do.
This gave me a sense of pride because I realized that I was reaching some students that I
had previously not reached.

As the unit progressed, I realized that the students were really gaining an
understanding of electricity. Before the unit began, the students were given a pre-test. At
the end of the unit, the students were asked the same questions on a post-test. On the pre-
test, one of the questions asked students to explain why a balloon that had been rubbed
against your hair can stick to a wall and not fall off? One of my higher level students
answered the pre-test question by saying, “When you rub a balloon against your hair it
creates static electricity. That electricity, then, can cling to the wall because it is looking
for a route towards the ground.” After the unit was complete he answered the same
question by saying, “When a balloon is rubbed against hair, it strips electrons from the
hair making the balloon negatively charged. Then, when the balloon is brought near the
wall, the wall becomes polarized. Since opposites attract, the balloon clings to the wall.”

A student who generally did not perform as well as the above student answered
the same question on the pre-test by saying, “The reason why a balloon can be rubbed
against your head and not fall off when you put it on the wall is because of static

electricity. It takes static energy from your hair/head and then goes onto the balloon

30

where the balloon sticks. The same student answered this question on the post-test by
saying, “A balloon that has been rubbed against your hair can stick to the wall because
you have just charged the balloon negatively. Then when you take the negatively
charged balloon near the neutral wall the charges in the wall are split up so that the
positive charges are pushed toward the surface of the wall while the negative charges are
pushed away from the surface. The opposite charges attract.” Even though this student
does not seem to understand it is only the positive and negative centers of charge that
migrate, her post-test answer is much improved.

Another question asked the students to explain the difference between current and
voltage. On the pre-test one of my lower level students said, “Current is when electricity
is moving, voltage is when it is stored.” After the unit had been completed, the same
student answered the question by saying, “Current is the flow of charge. Current is like
water while voltage is like the pressure that is necessary to get water to flow. So, it takes
voltage, specifically a difference in voltage across a circuit, to get current to flow.”

A higher level student answered the same question on the pre-test by saying,
“Current is different then voltage because voltage is the amount of electricity
(speed/power) in a circuit at a given time and current is ?” The same student answered
the post-test question by saying, “The difference between current and voltage is that
current is the flow of charge while voltage is the electrical pressure that is required to get
charge to flow.”

The hardest question on the test was question number fourteen. This question
asked students to describe the relationship between the voltage of a battery and the
voltage across each resistance in a series circuit and in a parallel circuit. One of my

highest level students answered the question on the pre-test by saying, “I don’t know.”

31

He answered the same question on the post-test by saying, “The voltage drop across each
resistance in a series circuit will add up to the voltage of the source. In a series circuit the
voltages are divided up among the resistors, because each resistor is not booked up to
positive and negative terminal of the battery. In a parallel circuit, the voltage drop across
each branch of the circuit is the same as the voltage of the source. This is because each
branch of the parallel circuit is connected to both the positive and the negative terminal of
the battery.

A lower level student answered the same question on the pre-test by also saying,
“I don’t know.” His answer improved on the post-test when he stated, “The voltage
across each branch in a parallel circuit is going to be the same as the voltage of the
battery. The voltage across the resistors in a series circuit gets split up so that the
voltages across the resistors is less than the voltage of the battery.” Even though this
student did not state that the voltage drops across each resistor in a series circuit added up
to the voltage of the battery, his post-test answer illustrates an understanding of the basic
concepts.

I saw answers similar to these again and again on the pre-test and post-test. I was
amazed by the number of misconceptions that students came into the unit with and how

they were able to reshape those erroneous thoughts into a correct conceptual fiamework.

32

Discussion and Conclusion

The goal of this unit was to improve the students’ conceptual understanding of
electricity by using a constructivist approach to its instruction. After reflecting on the
results, I believe that the goal has been met. Student test scores improved an average of
70.4% from the time students took the pre-test to the time they took the post-test. The
majority of the questions on the test required students to apply knowledge that they had
gained during the unit. Therefore, the data indicate that students reshaped their
preexisting knowledge and misconceptions to gain a better conceptual understanding of
electricity.

I firmly believe that the most influential part of the unit was the labs and hands-on
activities that the students performed. These activities required sustained mental activity
fi'om the students while often creating dissatisfaction with or a questioning of previous
knowledge. This forced the students to reevaluate and modify their ideas about
electricity. While some students do this with a more traditional approach, I believe that
more of my students were actively involved in thinking about the labs and modifying
their conceptual fi'amework to incorporate the new information into it. In addition, the
labs provided students with relevant applications in social contexts. Students were able
to talk about their discoveries and help one another get past stumbling blocks. Without
these activities, I believe the test scores would have been significantly lower.

While I felt the unit was a successful overall, the one major drawback was the
length of time it took to cover the unit. I found that labs and activities often took longer
for the students to work through than I had anticipated. In order to provide students with
ample time to get through the lab and share their results and discoveries with the class,

we often had to spend a day and a half or more to finish working with the material.

33

Therefore, where I may have given the students the formula for Ohm’s law and discussed
the relationships between current, voltage, and resistance in twenty rrrinutes, we spent
two days in class performing a lab on deriving Ohm’s law. At the end of the lab, I am
sure that students had a much better understanding of where the law came from and how
the three variables related to one another. However, I did not teach all of the material
that was dictated by the physical science curriculum for the semester. While most
students gained a deep understanding of electricity, they did so to the detriment of
learning about other topics.

Since I completed the unit in the spring of 2004 and did not write my thesis until
the spring of 2005, I was able to modify some of the electricity unit to teach it in a
timelier manner. I scaled back on the number of labs that the students did, performing
many as demos in front of the class. Some of the labs, like the Ohm ’s Law for Series
Circuits and Parallel Circuits were scrapped altogether because of their length.
Consequently, I was able to introduce the entire physical science curriculum.
Unfortunately, the average test score for this unit using the same post-test dropped from
an 84.2% during 2004 to a 71.2% in 2005. Based on this comparison, it appears that
decreasing the number of labs and hands-on activities caused the test score to drop
thirteen percent. Some of this drop may be attributable to the students I had this year. As
a whole, they were less motivated than the class I had in 2004. A quick perusal of my
gradebooks shows more zeros for assignments in 2005 than 2004. More importantly,
however, is the fact that I covered the same amount of material in less time. The students
did not perform the same number of labs and as a result they were not forced to consider
many of the topics in as much detail as the previously year. Consequently, this year’s

students, in my opinion, did not walk away with the same level of basic understanding of

34

electricity as last year’s students.

This poses a serious dilemma for me. On one hand, I know that it is important for
my students to have a deep conceptual understanding of the topics in which we engage.
On the other hand, I know that I need to make my way through a certain amount of
material by the end of the year. In order to maintain a balance between teaching for
understanding and getting through the entire curriculum, I plan on cutting out all
activities that are not specifically addressed by the Michigan Curriculum Framework
(MCF). As a result, next year I will have my students complete the labs on the electrical
current portion of the unit. Since electrostatics is not stressed in the MCF, I will perform
some demonstrations with the Van de Graaff generator to give them a basic
understanding of electrostatics. All other labs dealing with electrostatics will be cut out

of the unit.

35

APPENDICES

Appendices A: Electricity Unit Student Work

36

 

 

 

Physical Science Name:

Electricity Unit

Electrostatics Mini-Labs Date: Hour:
Purpose

To determine ways that objects can become charged and discharged.

Materials

Stocking, Polyethylene Bag, Plastic Box, Puffed Rice, Aluminum Foil, Fur, Burette,
Funnel, Water, Ebonit’e Rod, Ping-Pong Ball, Comb, Newspaper, Alluninum Pie Pan,
Balloon, Pre-Made Wire “Palm-Tree”, Wool, Silk Thread, Chair, Sharpened Pencil

Discussion

All objects are made fi'om atoms that contain electrical charges. Every atom consists of
both positively charged protons and negatively charged electrons. Generally, objects
contain the same number of protons and electrons and are, therefore, neutral. It is
possible, however, to transfer electrons from one object to another. When this occurs, an
imbalance of charge results. The object that has lost the negatively charged electrons
becomes positively charged while the object that has gained electrons becomes
negatively charged.

The term given to the study of charged particles is called electrostatics. During this
activity, you will be looking at various ways objects can become charged and discharged.

Procedure

Fill The Stockgzg

Step I . Hold the toe of the stocking and place the stocking against the wall.
Step 2. Rub the bag back and forth across the stocking 10 times.

Step 3. Pull the stocking away from the wall and hold it in the air.

Step 4. Record your observations.

What happens to the stocking when it is pulled away from the wall?

 

 

Electrostatic Jumping Beans
Step 1. Rub the cover of the box vigorously with wool.

Step 2. Record your observations.

What happens to the objects in the box when the box top is rubbed?

 

 

37

Magical Water

Step 1. Make sure the stopcock of the burette is closed. The “handle” should be parallel
with the desktop.

Step 2. , Use the funnel to fill the burette with water.

Step 3. Rub the ebonite rod vigorously with fur.

Step 4. Open the stopcock slowly until a thin stream of water emerges.

Step 5. Place the rod near the water but do not allow the two to touch.

Step 6. Record your observations (Try also turning the stopcock so that the water drips
out drop by drop)

What happens to the water as the rod approaches it?

 

 

The Obedient Ping Pong Ball

Step I . Place the ping pong ball on the table top.

Step 2. Rub the comb briskly with wool.

Step 3. Bring the comb near the ball without touching it.
Step 4. Record your observations.

What happens to the ping pong ball as the comb is brought near it? Can you control the
motion of the ball?

 

 

The Dry Newspaper

Step I . Rub the newspaper with the clear polyethylene bag vigorously for 30 seconds.
Step 2. Place the aluminum pie pan in the center of the newspaper.

Step 3. Pick the newspaper up by its edges.

Step4. Have someone else quickly touch the metal top.

Step 5. Record your observations.

What happens as you move your finger toward the metal on top of the newspaper?

 

 

The Palm Tree

Step 1 . Rub the balloon briskly with wool.

Step 2. Hold the palm tree by the glass tube and bring it near the balloon.
Step 3. Touch the wire “trunk” of your tree to the balloon.

Step 4. Record your observations.

What happens as the balloon is brought near your palm tree?

 

 

38

The Tricky Thread

Step 1. Rub the comb vigorously with wool.

Step 2. Move approximately 12 inches of silk thread near the comb until they touch.

Step 3. Draw the comb up and away fiom the thread slowly so that the thread and comb
become separated.

Step 4. Continue to move the comb up slowly

Step 5. Record your observations.

Can you control your piece of thread? How?

 

 

Magic Fingers

Step 1. Place a pencil on the back of a chair so that it is balanced.
Step 2. Rub your feet against the carpet.

Step 3. Draw your finger toward the graphite point of the pencil.
Step 4. Record your observations.

What happened to the pencil as you brought your finger toward it?

 

 

Note: Portions of this lab were adapted from Graf, Rudolf F. Safe and Simple Electrical
Exmriments. Toronto: General Publishing Company Ltd., 1964.

39

 

 

 

Physical Science Name:

Electricity Unit

Charged Grains Lab Date: Hour:
Purpose

To observe some of the effects of static electricity

Materials
Wire clothes hanger, puffed rice coated with aluminum foil, silk thread, comb, wool,
glass rod, silk, 2 rubber balloons, saran wrap

Discussion

All matter has a fraction of its electrons in a relatively loosely held state. When bodies
touch each other or come into close contact by rubbing, the surface electrons from one
body “get loose” and move to the other surface. The bodies are no longer neutral; the one
which gains electrons becomes negatively charged and the other body that has lost
electrons becomes positively charged.

Different materials have different affirrities for gaining or losing electrons. Glass rods
lose electrons when rubbed against silk leaving the glass with a positive charge. Combs
gain electrons when rubbed against wool leaving the comb with a negative charge.

In generating electric charges, fiiction does not create more electrons. Electrons simply
move between surfaces, keeping their total number the same. Electrons get redistributed
and are not created or destroyed.

As with any electrostatic experiment, weather plays a critical role. Experiments work
best when the weather is cool and dry. On damp summer days, electrons can “leak” off
charged objects causing the experiments not to work properly.

Procedure

Step 1. Hang one of the aluminum foil coated grains out of the way.
Step 2. Rub a comb with a piece of wool.

Step 3. Touch the grain with the comb.

Step 4. After touching the grain, move the comb toward it once again.

1. After touching the grain initially can you touch it again?

 

 

Step 5. Bring the wool that you rubbed the comb with near the grain.

40

2. What happens as the wool is brought near the grain?

 

 

 

Step 6. Touch the grain with your finger.
Step 7. Rub the glass rod with the piece of silk and touch the grain with the rod.
Step 8. After touching the grain, try to touch it again with the glass rod.

3. What happens to the grain?

 

 

Step 9. Bring the silk that you rubbed the rod with near the grain.
4. What happens as the silk is moved near the grain?

 

 

Step 10. Touch the grain with your finger.

Step 11. Charge the comb by rubbing it with wool and the glass rod by rubbing it with
silk.

Step 1 2. Charge the grain by touching it with the comb.

Step 13. Bring the glass rod toward the grain.

5. What happens and what general conclusion can be drawn from this?

 

 

 

Step 14. Pull the second aluminum foil covered grain down so that both grains are
hanging side by side.

Step 15. Charge the comb by rubbing it with wool.

Step 16. Touch one of the grains with the comb and then move the comb away.

6. What happens when you do this? Why?

 

 

 

Step I 7. Touch one of the grains with your finger and remove your finger immediately.

41

7. What happens and why?

 

 

 

8. How do you think that the aluminum covered grains could be used to determine
whether the charge on an object was positive or negative?

 

 

 

 

 

Step 18. Move one of the aluminum covered grains out of the way.

Step 19. Blow up the two balloons.

Step 20. Charge one of the balloons negatively by rubbing it with wool.

Step 21. Charge the other balloon positively by rubbing it with saran wrap.

Step 22. Hold a balloon in each hand and approach the single grain from both
sides. Once the grain begins to move stop moving the balloons and
observe.

9. What happens to the grain? Why?

 

 

 

 

Note: Portions of this lab were adapted fi'om Graf, Rudolf F. Safe and Simple Electrical
Experiments. Toronto: General Publishing Company Ltd., 1964. 21-23.

42

 

 

 

Physical Science Name:

Electricity Unit

Electroscope Lab Date: Hour:
Purpose

To determine how to use an electroscope. To charge the electroscope by contact and
induction

Materials
Electroscope, rubber rod, wool, glass rod, silk

Discussion

An electroscope is a device that is used for determining the presence of electrostatic
charges. It indicates the existence of charges on objects brought near it, and it can also
indicate the type of charge on that object.

The electroscope consists of an aluminum foil ball that is attached to a stiff piece of wire.
The wire passes through a cork attached to a flask. Light metal leaves rest on the bottom
of the stiff wire. The flask is used to assure that air currents do not disturb the sensitive
leaves.

As with any electrostatic experiment, weather plays a critical role. Experiments work
best when the weather is cool and dry. On damp summer days, electrons can “leak” off
charged objects causing the experiments not to work properly.

Procedure

Part A. Charging by contact

Step 1. Discharge the electroscope by touching the aluminum foil ball with your finger.
Step 2. Rub the rubber rod with wool. Touch the rod to the aluminum foil ball.

1. What happens to the leaves of the electroscope?

 

 

2. What charge is on the leaves and hpw do you know this? (Think of previous labs)

 

 

 

 

 

43

Step 3. Discharge the electroscope by touching the foil ball with your finger.
Step 4. Charge the rubber rod with wool.
Step 5. Bring the charged rod near the foil ball but do not touch it.

3. What happens when the charged rod is placed near the foil ball?

 

 

4. What happens when the charged rod is moved away from the foil ball?

 

 

5. How does this differ from when the charged rod touched the foil ball? Why do you
think that this difference occurs?

 

 

 

 

Part B. Charging by In_duction

Step 6. Devise a way to leave a charge on the electroscope using the charged rubber rod
without touching the rod to the foil ball. This means that the leaves of the
electroscope should remain partially separated once the rod is removed.
Remember, you cannot touch the foil ball with the rod! (Call me over to show
me how to do this when you have successfully accomplished this)

6. Explain how you charged the electroscope in step 6.

 

 

 

 

 

7. What charge is placed on the leaves of the electroscope in step 6? How do you know?

 

 

 

 

 

8. Now that the electroscope is charged, what would happen to the leaves if you brought
a positively charged object near the foil ball? How about a negatively charged object?

 

 

 

 

 

Note: Portions of this lab were adapted from Graf, Rudolf F. Safe and Simple Electricgl
Experiments. Toronto: General Publishing Company Ltd., 1964. 11-14.

45

 

 

 

Physical Science Name:

Electricity Unit

Electrophorus and Leyden Jar Lab Date: Hour:
Purpose

To use a device that can produce a large number of successive charges of static
electricity. To create an object for storing electrical charge.

Materials
Electrophorus, wool, electroscope, rubber rod, neon circuit tester, plastic drinking glass,
aluminum foil, plastic comb, paper clips.

Discussion

An electrophorus is a device that is capable of producing a large number of successive
charges of static electricity. The electrophorus that we will be using is a phonograph
record. An aluminum pie pan with an insulated handle will be placed against the
electrophorus in order to acquire a charge. Whenever the aluminum pie pan is
discharged, one can simply place the pie pan back onto the record to charge it once again.

The electrophorus is particularly useful because it can be used to charge a Leyden Jar. A
Leyden jar is a device that can be used to store electrical charges. Prior to the
development of the Leyden jar, many methods of producing electric charges had been
discovered; however, there was not a method for storing these electric charges. In this
experiment, you will build a Leyden jar similar to the first one built in 1745.

Procedure
Part A - Using the electrophorus

Step 1. Place the record on a flat surface and rub the surface with wool vigorously for at
least 30 seconds

Step 2. Hold onto the handle of the pie pan and place it onto the electrophorus (record).
Once the pie pan is on the record place a finger on the pie pan.

Step 3. Remove your finger.

Step 4. Lift the pie pan off the electrophorus.

Step 5. Touch the aluminum pie pan with your finger.

I. What happens when you bring your finger near the charged pie pan?

 

 

Step 6. Charge the electroscope negatively by touching the foil ball with a rubber rod that
has been rubbed with wool.

Step 7. Repeat steps 2 - 4 to recharge the electrophorus

Step 8. Bring the electrophorus near the electroscope without touching it.

46

2. What charge does the electrophorus have and how do you know?

 

 

 

3. Explain how the pie pan becomes charged. (Careful — This takes some thought)

 

 

 

 

Step 9. Repeat steps 2 — 4 to recharge the electrophorus.

Step 10.

Hold onto one of the terminals of the neon circuit tester. Bring the other
terminal near the electrophorus.

4. What happens when the electrophorus is brought near the neon circuit tester?

 

 

PartB—

Step I I.
Step 12.

Step 13.
Step 14.

Step I 5.
Step 16.
Step I 7.
Step 18.
Step I 9.
Step 20.

Step 21.
Step 22.

Building and using the Leyden jar

Tear off a square of aluminum foil big enough to wrap around the outside of the
plastic drinking glass.

Neatly wrap aluminum foil around the outside of the plastic drinking glass. The
foil should cover the bottom of the cup and come three quarters of the way up.
Remove the foil from the outside of the cup. Place the foil inside the cup.
Repeat steps 11 — 12. This time leave the aluminum foil on the outside of the
cup.

Attach enough paper clips together so that they will make a chain that can reach
from the top of the cup to the bottom of the cup.

Attach the first paper clip to the comb such that the top of the paper clip sticks
above the comb.

Lay the comb across the top of the cup.

Repeat steps 1 — 4 to recharge the pie pan.

Touch the charged pie pan to the top paper clip of the Leyden jar.

Repeat steps 2 - 4 to recharge the pie pan. Again touch the charged pie pan to
the top paper clip.

Repeat step 20 another six times

Place one end of the copper wire against the foil on the outside of the cup.
Bring the other end of the wire toward the top paper clip.

5. What happens when the wire touches both the outside of the cup and the paper clip?

 

 

47

Step 23. Repeat steps 18 — 21 to recharge the Leyden jar.
Step 24. Hold one of the terminals of the neon circuit tester against the outer aluminum
foil. Touch the other end to the top paper clip.

6. How does this flash of light compare to the flash of light produced by the
electrophorus?

 

 

7. What conclusion can you draw from this?

 

 

 

Step 25. Experiment on your own. Here are a few things to try. First, recharge the
electrophorus. If you touch the outer layer of foil and the paper clip you should
receive quite a shock. How does this shock compare to touching the
electrophorus after it has been charged. Another thing you can try is to hold
onto the outer layer of foil as you charge the electrophorus. When discharged,
you should notice an even bigger shock.

Note: Portions of this lab were adapted from Graf, Rudolf F. Safe and Simple Electrical
Experiments. Toronto: General Publishing Company Ltd., 1964. 16 — 20.

48

A-5

 

 

 

Physical Science Name:

Electricity Unit

Flowing Water Mini Lab Date: Hour:
Purpose

To determine why and how water flows.

Materials
Bottles(3), rigid plastic tubing, flexible rubber tubing, c10thespin(2), water, beaker

Procedure

Step 1. Connect the two sirrrilar sized bottles together with the flexible rubber tubing.

Step 2. Place one clothespin on the flexible tubing to pinch it off. Attach the second
clothes pin to the first to form a tight seal.

Step 3. Fill the beaker with water.

Step 4. Transfer water from the beaker into one of the bottles.

Step 5. Remove the clothespin and observe.

1. When does the water stop flowing out of initial container of water?

 

 

Step 7. Dump the water out of each container.

Step 8. Remove one of the containers and replace it with the container that is a different
size.

Step 9. Repeat steps 3 — 6.

2. How does this trial compare with the one from above?

 

 

3. Make a generalized statement about what is necessary for water to flow.

 

 

 

 

Note: Portions of this lab were adapted from 700 Science Exmriments For Everyone.
New York: Delacorte Press, 1958. 168.

49

A-6

 

 

 

Physical Science Name:

Electricity Unit

Current Lab Date: Hour:
Purpose

To determine how to create and detect an electrical current.

Materials
Galvanoscope, copper (2), zinc (2), wires (3), cups (2), distilled water, tap water, salt
water, sugar water, felt, lemon,

Discussion

The earth’s magnetic field aligns the magnetized needle of a compass in a North-South
position and holds it there. The compass needle remains stationary as long as a current
carrying wire is not placed near the compass. However, a compass placed over a current
carrying wire will cause the needle of the compass to deflect. The current carrying wire
creates another magnetic field, which, in addition to that of the earth’s, affects the
position of the compass needle.

Electric current is invisible, but it can be detected with a device known as a
galvanoscope. A galvanoscope is a device that utilizes the fact that current flowing in a
wire will deflect a compass needle. A galvanoscope amplifies this effect because many
turns of wire are placed around a compass. Thus, the current in each wire is added to that
of every other wire. As a result, a galvanoscope is capable of creating a magnetic field
that is greater than that generated by a single current carrying wire. Consequently, one
can detect very small currents with this device.

To use the galvanoscope, it should be placed so that the needle is aligned with the North
and South poles. The two wire leads should then be connected to the object that is being
tested. A deflected compass needle indicates that current is flowing in the circuit being
tested. If there is not a deflection, then current is not flowing in that circuit.

Procedure

Step 1. Sand the copper and zinc metal. Each metal should be shiny before you start.

Step 2. Connect two wires to the wire leads of the galvanoscope.

Step 3. Orient the compass so that the needle is aligned with the North and South poles.

Step 4. Connect the zinc to one of the free ends of the wire with an alligator clip.

Step 5. While watching the galvanoscope, connect the copper to the other wire with an
alligator clip. If the needle deflects, then current is flowing. If it does not
deflect, there is no current. Record your observations in the table.

Step 6. Connect the two pieces of metal with a wire to form a complete loop. Record
your observations.

Step 7. Disconnect the wire that you attached in step 6.

Step 8. Pour distilled water into one of your cups.

Step 9. Place the two metals into the cup of distilled water. Make sure that the
metals do not touch one another. Record your observations.

50

Step 10.
Step I 1.
Step 12.
Step 13.
Step 14.

Step 15.
Step I 6.

Step 17.

Step 18.

Step 19.

Step 20.

Step 21.

Step I 6.

Step I 7.
Step 18.

Pour the distilled water down the drain and replace it with tap water.

Place the two metals into the cup of tap water and record your observations.
Remove the metals from the tap water.

Pour a fair amount of salt into the cup with the tap water.

Place the two metals back into the cup making sure that they do not touch one
another. Record your observations.

Remove the zinc metal from the cup.

Connect the remaining piece of copper and zinc together with a wire.

Fill the second cup with tap water and add a fair amount of salt.

Place the piece of copper and zinc that you just connected into the two cups of
salt water. The zinc should go into the cup that already contains the piece of
copper. The new copper piece should go into the fresh cup of salt water.
Place the piece of zinc that you removed fi'om the first cup in step 15 into the
second cup of salt water. Record your observations.

Remove all the metals from the cups.

You may take the piece of zinc and copper that are not connected to the
galvanoscope and set them to the side. You will no longer need them. You
may also dump out 93 of the cups of salt water.

Place the piece of felt into a cup with salt water and allow it to soak for a
minute.

Remove the felt and squeeze it so that the excess water is removed.

Place the felt between the copper and zinc. Apply light pressure to the top
metal. Record your observations.

Step19. Remove the felt and place it to the side.
Step20. Replace the zinc metal with the other piece of copper metal. You should now

Step2] .

Step 22.
Step23.

Step24 .
Step25 .
Step26 .

Step2 7 .

Step28 .
Step29 .
Step3 0 .
Step 31.

have two pieces of copper attached the galvanoscope.

Place the two pieces of copper into the salt water making certain that they do
not touch. Record your observations.

Remove both pieces of copper fi'om the salt water.

Replace the pieces of copper with pieces of zinc. You should now have two
pieces of zinc connected to the galvanoscope.

Place the two pieces of zinc into the salt water and record your observations.
Remove the two metals from the cup and pour the salt water down the drain.
Remove one of the pieces of zinc and replace it with copper. You should now
have a piece of zinc and a piece of copper connected to the galvanoscope.
Rinse the cup out with distilled water. After rinsing, fill the cup with distilled
water.

Pour a fair amount of sugar into the cup with distilled water.

Place the two metals into the cup and record your observations.

Remove the two metals from the cup. Pour the sugar water down the drain.
Place the two pieces of metal into an apple. The pieces of metal should be
close to one another, but should not touch. Record your observations.

51

Results

 

 

 

 

Current Detected Amount of Needle
(yes or no) Deflection (°)
Zinc and copper
Zinc and copper connected in
a complete circuit
Zinc and copper in distilled
water

 

Zinc and copper in tap water

 

Zinc and copper in salt water

 

Zinc to copper to zinc to
copper in salt water

 

Zinc and copper separated by
salt water soaked felt

 

Copper and copper in salt
water

 

Zinc and zinc in salt water

 

Zinc and copper in sugar
water

 

Zinc and copper in apple

 

 

 

 

 

Conclusion

What conclusions can you draw about electric current? (What seems to be necessary for

current to flow? When did the most current flow? Why can current flow through some
liquids but not others?, etc.)

 

 

 

 

 

 

 

 

 

Note: Portions of this lab were adapted from Graf, Rudolf F. Safe and Simple Electrical
Exmp’ments. Tomato: General Publishing Company Ltd., 1964. 75 - 7

52

A-7

 

 

 

Physical Science Name:

Electricity Unit

Resistance Lab Date: Hour:
Purpose

To investigate resistance to current flow.

Materials
D-cell batter holder, D-cell battery (2), Pencil, wire (3), flashlight bulb, bulb holder, Play-
Doh, multimeters (2), ruler or sheet of paper with a 10 cm mark

Discussion

When a flashlight bulb is connected to a battery, a current will flow through the bulb
which will heat its filament and cause it to light up. If we can control this flow of
current, we can then control the amount of light we will get from our bulb. If we have
less current, we will get less light. In order to get less current, we must impede its flow
by inserting some sort of resistance which will resist or impede the flow of current. Such
a device is called a rheostat.

The rheostat helps control the current in radios to change the loudness of the sound we
get fiom them, in motors to change their speed, in appliances to change their heat output,
and in theatre lights to make them grow brighter or dimmer.

Procedure

Part A - Resistance with pencil lead

Step 1. Connect one end of a shaved pencil to the negative terminal of a battery using a
wire. Connect one light bulb terminal to the positive side of the battery using a
wire. Connect the other terminal of the light bulb with another wire. Move the
free end of this wire along the length of the pencil lead.

1. What happens to the flashlight bulb as the two alligator clips move away from one
another?

 

 

Part B — Resistance with Play-Dob

Step 2. Roll Play-Dob into 4 different sized cylinders that range in diameter fi'om
1.0 — 2.0 cm. Each cylinder should be at least 14 cm in length. The quality
of the experimental results will depend strongly on the uniformity of
the cylinders. Maintain the same diameter over the entire length and
avoid cracks or voids in the Play-Dob.

Step 3. Connect the circuit so an alligator clip lead connects the positive terminal of the
battery holder to the red lead of a multimeter. Another alligator clip lead should
be connected to the black lead of the multimeter. The multimeter should be set to

53

Step 4.

Step 5.

Step 6.

Step 7.

Step 8.
Step 9.

the current firnction. Another alligator clip lead should be connected to the
negative terminal of the battery.

Place one of the Play-Doh cylinders into the circuit. It should be pushed into the
two alligator clip leads that are not connected to anything.

Set the second multimeter to the voltage function.

Place the two leads from the second multimeter into the Play-Doh 10 cm apart.
The black lead should be inserted into the negative end while

the red lead should be inserted into the positive end. If you do this correctly, the
multimeter reading will be positive. If you reverse the leads, the value the
multimeter gives you will be negative.

Record the current and voltage readings simultaneously. The current is found on
the multimeter that is attached to the circuit with alligator clips. The voltage is
found on the multimeter whose probes are stuck into the Play-Dob.

Remove the Play-Dob from the circuit.

Repeat steps 4 - 8 with the remaining Play-Dob cylinders.

Step 10. Determine the resistance of each Play-Doh cylinder by dividing the voltage in

volts across the Play-Dob by the current in amps running through the Play-Dob

 

Results
Play-Dob Voltage (V) Current (mA) Current (A) Resistance
Diameter (cm) (0)

 

 

 

 

 

 

 

 

 

 

Make a graph of the resistance (y-axis) vs. the diameter of the play-dob (x-axis).

Conclusions

2. How does the length of a resistor affect the current of a circuit? Explain how you
know this and explain why this occurs. (Reflect on Part A)

 

 

 

 

 

3. What mathematical relationship between resistor diameter and resistance does the
graph illustrate?

 

 

54

 

4. Briefly summarize the findings of this lab. Specifically, how does the resistor length
and the resistor diameter affect the resistance and the current in a circuit.

 

 

 

 

 

 

Note: Portions of this lab were adapted from Watson, George.
http://www.Lhysics.udel.edu/~watson/scenl 03/colloq2COO/problems/plavdohegrt.html

55

A-8

 

 

 

Physical Science Name:

Electricity Unit

Cells in Series and Parallel Date: Hour:
Purpose

To determine the advantages and disadvantages of cells connected in series and in

parallel.

Materials
Cups (3 ), salt water, multimeter, zinc and copper electrodes, wires

Discussion

Batteries can be connected together in one of two ways. A series connection occurs when
the positive electrode of one cell is attached to the negative electrode of a second cell. A
parallel connection occurs when the positive electrode of one cell is connected to the
positive electrode of the other cell while the negative electrodes of the two cells are also
connected.

When zinc and copper are the two electrodes, zinc is the negative electrode and copper is
the positive electrode. The salt water acts as an electrolyte solution that allows charge to
flow through the liquid.

Procedure
Part A — Cells in Series

Step 1. Sand all of your electrodes.

Step 2. Fill a glass with 150 mL of tap water and add 1 tbsp of salt.

Step 3. Place one copper and one zinc electrode into the salt water making sure they do
not touch one another.

Step 4. Set the multimeter to measure voltage.

Step 5. Touch the black lead of the multimeter to the zinc electrode and the red lead fi'om
the multimeter to the copper electrode. Record the voltage in the data table.

Step 6. Repeat step 2 and add a second cell by filling another cup with salt water. Place
a copper and a zinc electrode in this cup as well.

Step 7. Connect the zinc electrode from one cup with the copper electrode from the other
cup.

Step 8. Place the black multimeter lead against the piece of zinc that is not attached to a
wire. Place the red lead against the copper electrode without a wire. Record the
voltage in the data table.

Step 9. Add a third cell by filling a third cup with salt water. Add your last copper and
zinc electrodes to this cup.

Step 10. Connect the metal without a wire in the second cup to the opposite metal in the

last cup.

Step I 1. Repeat step 8 to determine the voltage of the three cells in series.

56

 

 

 

 

 

 

Part B — Cells in Parallel

Step 12. Remove the metal electrodes from two of the cups. Disconnect the wires from
these electrodes.

Step 13. Measure the voltage of the two electrodes in the first cup. Once again, place the
black lead against the zinc and the red lead against the copper. Record your
voltage.

Step 14. Add a second cell by placing a zinc electrode and a copper electrode into a
second cup of salt water.

Step 15. Connect the two pieces of zinc together with a wire and the two pieces of
copper together with a wire.

Step I 6. Measure the voltage by placing the red lead of the multimeter against a copper
electrode and the black lead against the zinc electrode in the same cup. Record
your voltage.

Step I 7. Add a third cell by adding a third cup of salt water. Place the remaining zinc
and copper electrodes into the solution. Connect the zinc electrode to the zinc
electrode in the middle cup and the copper electrode to the copper electrode in
the third cup.

Step I 8. Repeat step 17 and record the voltage.

Results

Cells in Series Cells in Parallel
it of cells voltage (v) # of cells voltage (v)
1 l
2 2
3 3

 

 

 

 

0 Make a graph of voltage vs. the number of cells connected in series using Excel.
It should be an XY scatter-plot. Place the # of cells in the first column and the
voltage in the second column. When complete, add a linear trendline.

0 Make a graph of voltage vs. the number of cells connected in parallel using Excel.
It should be an XY scatter-plot. Place the # of cells in the first column and the
voltage in the second column. When complete, add a linear trendline

57

 

Conclusions

1. How does the number of cells connected in series affect the voltage of the system?

 

 

 

2. How does the number of cells connected in parallel affect the voltage of the system?

 

 

 

3. What is an advantage of adding cells in series?

 

 

 

4. A remote control car requires 12 volts to operate. How many 1.5 volt batteries would
be necessary to power the car? How must the batteries be arranged?

 

 

 

5. How do you think the addition of cells in parallel affects the longevity of these cells?
Will they last for a longer time or a shorter time? Why do you think this?

 

 

 

 

Note: Portions of this lab were adapted from Cunnigham James and Norman Herr.
Hands-On Physics Activities with Real-Life Applications. New York: The Center for
Applied Research in Education, 1994

58

 

 

 

Physical Science Name:

Electricity Unit

Circuits in Series and Parallel Lab Date: Hour:
Purpose

To determine how various arrangements of flashlight bulbs affect bulb brightness.

Materials
D-Cell, D-Cell battery holder, connecting wire, 3 flashlight bulbs, 3 bulb holders,

Discussion

A dry cell, commonly called a battery, is a source of electrical energy. Many
arrangements are possible to get this energy fi'om dry cells to flashlight bulbs. Series
circuits have a single pathway through which electrons can move while parallel circuits
have multiple pathways for electrons to move through.

Procedure

Step 1. Arrange one bulb (without a holder), one battery, and up to two bare wires in as
many ways as you can to make the bulb emit light. Sketch each of your
successful arrangements below.

1. Describe the similarities among your successful trials.

 

 

 

 

Step 2. Screw one of the bulbs into a bulb holder.
2. What two parts of the bulb does the holder make contact with?

 

 

59

Step 3. Connect one bulb to two D-Cells. Note the apparent brightness of the bulb.
Step 4. Connect a second bulb in series to the circuit. Note the apparent
brightness of the bulb.
Step 5. Connect a third bulb to the circuit in the same fashion. Note the apparent
brightness of the bulb.

3. Do the bulbs light in each of the series circuits you have designed?

 

4. Which circuit contains the brightest bulb or bulbs? The dirnmest bulb or bulbs? The
first, second, or third?

 

 

Step 6. In the circuit with 3 bulbs unscrew one of the bulbs. Screw this bulb back in and
unscrew a different one.

5. What happens when a bulb that is connected in series is unscrewed from its base?

 

 

Step 7. Remove the bulbs connected in series from the battery. Rearrange the bulbs such
that two bulbs are connected in parallel. Note the apparent brightness of the
bulbs.

Step 8. Add another bulb in parallel to the circuit. Note the apparent brightness of the
bulbs.

Step 9. Unscrew one of the bulbs in the circuit and observe. Screw this bulb back in and
unscrew a different bulb fiom the circuit.

6. Do the bulbs light in each of the parallel circuits you have designed?

 

7. Which parallel circuit contains the brightest bulb or bulbs? The dirnmest bulb
or bulbs?

 

8. What happens when a bulb that is connected in parallel is unscrewed from its base?

 

 

60

9. Summarize the differences between series and parallel circuits.

 

 

 

 

 

 

Note: Portions of this lab were adapted from Conceptual Physics Laboratog Manual.
USA: Addison-Wesley Publishing Company, Inc., 1987. 279 — 282.

61

A-IO

 

Physical Science Name:

Electricity Unit

Ohm’s Law Lab Date: Hour:
Purpose

To determine how voltage and resistance affect the current in a circuit.

Materials
2 Multimeters, 10 Resistors ranging from 330 - 1,0000, 4 D-Cell Batteries, D-Cell
Batter Holder, Wires, Switch

Discussion

In the early 1800’s, Georg Simon Ohm, a German physicist, developed the law that now
bears his name. He determined that electrical current is controlled by two variables:
voltage and resistance.

During this lab you will attempt to determine the relationship between current, voltage,
and resistance. To accomplish this, you will begin by maintaining a constant voltage.
You will then test different resistors and determine how they affect current. Later, you
will maintain a constant resistance. You will then test how different voltages affect the
current.

Procedure
Part A - Voltage vs. Current at constant Resistance

Step 1. Connect the circuit so that the negative battery terminal is connected to a switch.
Attach a 100 Q resistor to the other end of the switch. Attach the other end of the
resistor to the black lead of a multimeter. Finally, attach the red lead of the
multimeter to the positive terminal of the battery.

Step 2. Set the multimeter to the current function.

Step 3. Set the other multimeter to the voltage function.

Step 4. Close the switch.

Step 5. Place the leads of the 2'“1 multimeter against the ends of the resistor. If the leads
are reversed, the voltage reading will be negative.

Step 6. Measure the current and voltage simultaneously. Record the measurements in the
first data table.

Step 7. Repeat the above steps with a 2nd, 3'“, and 4th battery.

Part B — Current vs. Resistance at constant voltage.

Step 8. Turn the multimeter that you used to measure voltage to the resistance function.

Step 9. Measure the resistance of each resistor by touching the leads of the meter to
either end of the resistor. Do this while the resistor is not connected to anything.
Arrange the resistors in order of increasing resistance. Record the values in order
in the second data table.

62

Step 10. Choose the lowest valued resistor. Set up a circuit that is identical to the circuit
on the previous page. You will keep two D-Cells in the battery holder for the
rest of the lab. Change the multimeter back to the voltage firnction.

Step I 1. Close the switch and measure the current and voltage of the circuit
simultaneously. Record the measurements in the second data table.

Step 12. Repeat steps 10 - 11 for each resistor.

Results
Data Table # 1

# of Batteries Current mA Current A
l

 

2
3
4

Data Table # 2

Resistance 0 Current mA Current A

 

0 Using the first data table make a plot of voltage in volts vs. current in amps using
Excel. It should be an XY scatter-plot. Place the current measurements in the
first column and the voltage measurements in the second column. When
complete, add a linear trendline and determine the slope of this line.

0 Using the second data table make a plot of current in amps vs. resistance in ohms
using Excel. It should be an XY scatter-plot. Place the resistance measurements
in the first column and the current measurements in the second column. When
complete, add a power trendline.

0 Using the second data table make a plot of current in am 3 vs. l/mism“ in lAW",
using Excel. It should be an XY scatter-plot. Place the lmtsmcc values in the first
column and the current measurements in the second column. When complete, add
a linear trendline and determine the slope of the line.

Conclusions

1. What mathematical relationship between voltage and current does the graph illustrate?

 

 

63

2. What mathematical relationship between resistance and current do the graphs
illustrate?

 

 

3. What does the slope of the voltage vs. current graph represent? How closely does it
agree with the actual value? (Calculate the % error)

 

 

 

4. If a fifth D-Cell battery was added to the circuit for part A, what would you expect the
current to be for the circuit? Why?

 

 

 

5. What does the slope of the current vs. 1/,.,_.,isu..,wc graph represent? How closely does it
agree with the actual value? (Calculate the % error)

 

 

 

6. Did the potential difference across the resistor in part B change when you changed the
resistor in the circuit?

 

 

 

A-ll

 

 

 

Physical Science Name:

Electricity Unit

Ohm’s Law with Series Circuits Lab Date: Hour:
Purpose

To determine the relationships among the voltages, currents, and resistances in a series
circuit.

Materials
Multimeter (2), D-cell (2), D-cell battery holder, different resistors (3 ), switch,
connecting wire

Discussion

In a series circuit, the devices and the wires connecting them form a single pathway for
electron flow between the terminals of a battery. This means that resistors that are
connected in a series circuit must be connected together end to end. Electrons that flow
through this current leave the negative terminal of the battery, pass through each resistor,
and then return to the positive terminal of the battery.

Procedure

Step 1. Connect the circuit as you did in the last lab. Begin with the resistor of lowest
resistance. The multimeter should be set to the current function.

Step 2. Set the multimeter that is not being used in the circuit to the voltage function.

Step 3. Close the switch.

Step 4. Place the leads of the 2"d multimeter against the ends of the resistor. If the leads
are reversed, the voltage reading will be negative.

Step 5. Measure the current and voltage simultaneously. Record your measurements.
Calculate the resistance across Rt.

Current (I) = A Voltage (V) = V
Calculated Resistance R; = Q

1. How does the calculated value of the resistance compare to the manufacture’s rated
value? Calculate the % error.

 

 

Step 6. Modify the circuit to include a second resistor in series. Measure the current
between the positive battery terminal and the first resistor, between the two
resistors, and after the second resistor. Measure the voltages across the first
resistor, the second resistor, and both resistors. To measure the current at the 3

65

different locations you will need to detach the multimeter and reconnect it in the
correct spot. To measure the voltages you can simply touch the probes across

the correct resistors.
Current at A1 = A Current at A2 = A Current at A3 = A
Voltage V1 = V Voltage V2 = V Voltage V3 = V

4. How do the current readings compare?

 

 

5. How do the three voltage readings compare?

 

 

 

6. Calculate the values of R1 and R2. Show your work.

 

 

 

7. Divide V3 by the current. How does the result compare to the sum of the resistances
you calculated in part 6?

 

 

 

8. What is the relationship among the current in the circuit, the spm of the resistances,
and the voltage across Q the resistances?

 

 

 

Step 7. Record the manufacturer’s rating of each of the three resistors.
R1 = 9 R2 = 0 R3 = Q

 

 

Step 8. Arrange all three resistors, the switch, and the batteries in series. Close the
switch, measure and record the total voltage V4 across all three resistors.

V4: V

 

66

9. According to the manufacturer’s ratings, what is the total resistance in the circuit?

 

10. Predict what the readings will be for the multimeters measuring current at A1, A2,
and A3.

 

 

Step 9. Measure the current between the positive terminal and the first resistor, between
the first and second resistor, and after the last resistor. Also measure the voltages
across each individual resistor. Use the same technique as you did for step 6.

Current at A1 = A Current at A2 = A Current at A3 = A
Voltage V1 = V Voltage V2 = V Voltage V3 = V

11. How do your measured values of the currents through the multimeter compare to the
value you predicted in step 4?

 

 

12. Calculate the values of the resistances of R1, R2, and R3 from your current and
voltage measurements. Show your work.

 

 

 

13. Divide V4 by the current. How does the result compare to the sum of the resistances
you calculated in part 12?

 

 

 

Conclusions

14. How do the currents in different parts of a series circuit compare?

 

 

15. Describe the relationship among the voltage of the source and the voltages across
each resistance in a series circuit.

 

 

 

 

67

16. Describe how current relates to the sum of the resistances and the sum of the
voltages.

 

 

 

 

Note: Portions of this lab were adapted from Conceptual Physics Laboratory Manual.
USA: Addison-Wesley Publishing Company, Inc., 1987. 285 — 288.

68

A-l2

 

 

 

Physical Science Name:

Electricity Unit

Ohm’s Law with Parallel Circuits Lab Date: Hour:
Purpose

In a parallel circuit, the devices and wires are connected to two common points. This
means that resistors that are connected in a parallel circuit are connected such that the left
side of each resistor is in contact with one point in the circuit while the right side of the
resistor is in contact with a different point in the circuit. Electrons leaving the negative
terminal of a battery can travel through any branch of the circuit. There are multiple
pathways that an electron may follow. However, a particular electron will flow through
one branch and then continue on to the positive terminal of the battery. A particular
electron does not leave the negative battery terminal, flow through at; branch, and then
return to the positive terminal.

 

Materials
Multimeter (2), D-cell (2), D-cell battery holder, resistors of equal resistance (2) different
resistor, switch, connecting wire

Procedure

Step 1. Connect the circuit as you did for the last lab. Begin with one of the resistors of

equal resistance. The multimeter should be set to the current frmction.

Step 2. Set the multimeter that is not being used in the circuit to the voltage function.

Step 3. Close the switch.

Step 4. Place the leads of the 2'"1 multimeter against the ends of the resistor to measure
the voltage drop across this resistor. If the leads are reversed, the voltage reading
will be negative.

Step 5. Measure the current and voltage simultaneously. Record your measurements.
Calculate the resistance across R1.

Current (I) = ._ A
Voltage (V) = _ V
Calculated Resistance R1 =

Step 6. Place a second resistor of gual resistance in parallel with the first resistor.

l. Predict whether the current measured at A3 will be greater than, less than, or the same
as the current measured in step 1.

 

2. Predict whether the voltage V; across the first resistor will be greater than, less than,
orthe sarneasit was instep l.

 

Step 7. Close the switch. Measure and record the current rrmning through the lSt resistor,
the second resistor, and through the battery. Also measure the voltage across
each resistor and across the entire circuit.

69

Current at A1 = A Current at A2 = A Current at A3 = A
Voltage V; = V Voltage V2 = V Voltage V3 = V
3. How do the three current readings compare?

 

 

4. How do the three voltage readings compare?

 

 

5. Calculate the values of resistances R. and R2 using Ohm’s law. Show your work.

 

 

 

6. Calculate the equivalent resistance of the circuit by dividing the voltage of the source,
V3, by the current through the source, A3. Show your work.

 

 

7. How does the equivalent resistance of the circuit compare with the two values you
calculated for the individual resistances in number 5.

 

 

 

Step 8. Change R2 so that R1 and R2 now have different resistances. The setup should be
identical to step 6 with the exception that you now have resistors of different
resistance in your circuit

Step 9. Repeat step 7. Measure and record the current and voltage at each of the

locations.
Current at A; = A Current at A2 = A Current at A3 = A
Voltage V1 = V Voltage V2 = V Voltage V3 = V

8. How do the three current readings compare?

 

 

9. How do the three voltage readings compare?

 

 

70

10. Calculate the values of resistances R1 and R2 using Ohm’s law. Show your work.

 

 

 

l 1. Calculate the equivalent resistance of the circuit by dividing the voltage of the

source, V3, by the current through the source, A3. Show your work.

 

 

12. How does the equivalent resistance of the circuit compare with the two values you
calculated for the individual resistances in number 5.

 

 

 

Conclusions

13. Describe the relationship among the currents in a parallel circuit.

 

 

 

14. Describe the relationship among the voltages in parallel branches of a circuit.

 

 

 

15. Describe the relationship among the equivalent resistance and the individual

resistances in a parallel circuit.

 

 

 

 

 

Note: Portions of this lab were adapted fi'om Conceptuial Physics Laboratogy Manual.
USA: Addison-Wesley Publishing Company, Inc., 1987. 289 - 293.

71

A-13

 

 

 

Physical Science Name:

Electricity Unit

Fuse Lab Date: Hour:
Purpose

To determine how a fuse can protect a circuit.

Materials
3 D-Cell batteries, insulated wires, flashlight bulbs, bulb sockets, switch, steel wool,
balloon, hook-up wire with stripped sections in the middle

Discussion

As electrical energy passes through a wire, some is converted into heat. The amount of
electrical energy released as heat is directly proportional to the current. In fact, the
amount of heat released is proportional to the square of the current. Therefore, if one
were to triple the current in a wire, it would give off 9 times (32) the amount of heat it
was originally giving off. Because the heating effect in wires increases as the square of
the current passing through them, wires in high current circuits can overheat and start a
fire.

Thomas Edison recognized the danger of excessive current and developed a device
known as the fuse. A fuse consists of a thin, special wire enclosed in a nonconducting
material. When current through a wire exceeds a certain amperage, the metal in the fuse
will melt, thereby opening the circuit before any real damage can occur.

Excessive current in a circuit can result from two different events. One such event is
called a short circuit. A short circuit results when wires on opposite sides of an appliance
touch, creating a low resistance pathway that allows current to bypass the appliance.
Current increases dramatically during a short circuit and can cause the wire in the fuse to
melt.

Another event that can result with excessive current is an overloaded circuit. You
learned in the last lab that as resistors are added to a parallel circuit the overall resistance
of the circuit lowers. According to Ohm’s law, as the resistance of a circuit decreases,
the current of the circuit will increase. Consequently, as more appliances are connected
together in parallel, current for that circuit will increase. If enough appliances are
connected, the heat produced from the current can cause the wire in the firse to melt and
“blow” the fuse.

Procedure

PartA-The Fuse

Step 1. Pull a couple of strands off the steel wool pad and roll these strands together.
Step 2. Connect the steel wool, one battery, and a switch together in series.
Step 3. Close the switch and observe. (if nothing happens, you have too much steel wool)

72

1. What happens when the switch is closed?

 

 

Part B — Short Circuits

Step 4. Repeat step one to create another steel wool fuse.

Step 5. Connect a fuse, switch, light bulb, and 1 battery together in series. Make
sure that each wire connected to the bulb holder has a bare section in the
middle of the wire.

Step 6. Close the switch and observe.

Step 7. Hold the bare sections of wire connected to either side of the light
bulb together.

2. What happens when the switch is closed initially?

 

 

3. What happens when the two bare sections of wire are touched together? Why does
this happen?

 

 

 

 

Part C — Overloading the Circuit

Step 8. Repeat step one to create another steel wool fuse.

Step 9. Connect 3 D-Cells together in series

Step 10. Connect the fuse in series to the positive terminal of the battery.

Step 11. Connect 3 bulbs in parallel to this circuit.

Step 12. Continue adding bulbs in parallel one at a time to the circuit. Continue until the
fuse “blows”. You may need to share bulbs with other groups for this step
depending on the size of your fuse.

4. How many bulbs were required to melt the fuse?

 

 

5. Why doesn’t the fuse blow initially? Why do you have to add more bulbs to get the
fuse to blow?

 

 

 

 

73

6. The fuse boxes of some older houses were not designed to carry the loads required by
modern appliances. To avoid continuously replacing fuses, some people replaced
fuses with copper pennies. Explain why this is extremely dangerous.

 

 

 

 

7. Why are fuses connected in series with the power supply while all the other appliances
are connected in parallel?

 

 

 

 

Exten_sion Question

8. The amperage rating for a fuse is stamped onto the fuse. The car fuse shown in the
first picture is rated at 15 amps. This means that a current of 15 amps can pass
through the fuse, but any additional current will cause the wire in the fuse to melt.
Explain how you could determine the amperage rating for your steel wool strand and
actually measure it if time permits.

 

 

 

Note: Portions of this lab were adapted from Cunnigham James and Norman Herr.
Hands-On Physics Activitier with Real-Life Applications. New York: The Center for
Applied Research in Education, 1994. 578 - 580.

74

A-l4

 

Physical Science Name:
Electricity Unit
Household Wiring Lab Date: Hour:

 

 

The following is text that accompanies the power point presentation.

Slide 1: How we will connect our circuit for class.

We will be wiring two receptacles, a switch, and a light. We want the receptacles to
work all of the time and the light to only work when the switch is turned on. Therefore,
we will wire a plug to one of the receptacles. We will then connect the next receptacle,
the switch, and finally the light.

Slide 2: Wiring a Receptacle

Receptacles can be wired in a number of ways. The way shown in the picture is similar
to the way we will do it. Notice that two large wires enter the electrical box: one from
above and one from below. Each of these large wires has three wires inside.

Slide 3: Wiring a Receptacle - # 2

Notice that each large wire contains a white wire, a black wire, and a bare copper wire.
The black wire is the “hot” wire (120 V), the white wire is the “neutral” wire (0 V), and
the bare copper wire is the “grounding” wire.

Slide 4: Wiring a Receptacle - # 3

If you are connecting the wires to the screw terminals, always connect the Black wire to
the Brass screw and the white wire to the silver screw. Pigtail the bare copper wires
together using a third, small piece of copper wire. Connect the ends of the copper wires
together in a wire nut and attach the fiee end of the pigtail to the green grounding screw.

Slide 5: Wiring a Receptacle - # 4
When using the push-in fittings in the back of the receptacle, always push the Black wires
into the side of the receptacle with the Brass screws. Push the white wires into the side of
the receptacle with the silver screws.

Slide 6: Wiring a Receptacle - # 5

We will use the push-in fittings on the back of the receptacle. To remove a wire from a
push-in fitting, place a screwdriver firmly in the release opening while simultaneously
pulling the wire out.

Slide 7: Wiring a Single Pole Switch

Single pole switches are used to control a light fi'om a single switch. As you can see
from the picture, they have two brass screws. The ones we will be using also have a third
green screw for grounding.

75

Slide 8: Wiring a Single Pole Switch - # 2

A single pole switch is used to turn an object, like a light, on or off. Unlike a receptacle
that has 4 screw terminals, a switch has two. Since our switch is in the middle of the
circuit, it will have two cables entering the box.

Slide 9: Wiring a Single Pole Switch - # 3

To wire our switch, you will need to connect the two black wires to the push-in fittings in
the back of the switch. Since the switch just opens or closes the circuit, you do not book
the white neutral wires to it.

Slide 10: Wiring a Single Pole Switch - # 4

After connecting the black wires, we need to connect the white wires. To do this, the
white insulation needs to be removed from the end of each wire. The wires then need to
be screwed into a wire nut together.

Slide 11: Wiring :1 Light Fixture
Our light fixture is at the end of the circuit. Therefore, we will only have one wire
entering the box.

Slide 12: Wiring a Light Fixture - # 2

Attach the black wire to the brass screw and the white wire to the silver screw. Attach
the bare copper wire to the green screw that is located inside the electrical box.

76

A-15

 

 

 

Physical Science Name:

Electricity Unit

Cost of Electricity Activity Date: Hour:
Purpose:

To determine how much it costs to use some of your favorite electrical devices over a
period of 30 days.

Discussion:

The power company sends your family a bill every month for the electrical energy that
your farrrily uses. The total cost of the bill is equal to the number of kilowatt-hours of
electricity you have consumed multiplied by the rate that the power company charges per
kilowatt-hour.

Procedure:
Step I . Determine the electrical rate the power company charges your family per
kilowatt-hour of electricity consumed.

1.

Step 2. Pick three electrical devices which are important to you. List those devices in the
table below.

Step 3. Determine the power rating of each of these devices in kilowatts. Record that
value in the table as well.

Step 4. Estimate the amount of time you use each device over the course of a day.
Multiply this value by thirty and record this value in the table.

Step 5. Multiply the power rating of the device in kilowatts by the amount of time the
device is used during the month. Record this value as the amount of energy used
in the data table.

Step 6. Multiply the energy consumed during the month in kilowatt hours by the rate the
power company charges you per kilowatt hour. Record the amount it costs to use

 

 

that electrical device in the table.
Electrical Power Rating Time Used Energy Cost to use
Device (kW) Per Month Consumed Device for the

(h) (kWh) Month (S)

 

 

 

 

 

 

 

 

 

77

 

1. What is the unit of charge?

A-l6

 

Physical Science Name:
Electricity Unit
Electricity Unit Study Guide Date: Hour:

 

 

. The electrical force between two charged particles depends on two things. What are
these two things?

 

. How does the electrical force change as charged particles are brought closer together?
Drawn further apart?

 

 

. What is the charge of an electron? A proton? What happens when these particles are

brought near one another?

 

 

. What are three methods by which an object can become charged?

 

. Through which method is charge transferred when a comb is rubbed through your
hair? The comb becomes charged how (+ or -)? Your hair becomes charged how?

 

. Explain what is meant by electrical polarization. (This is the same thing as charging
by induction)

 

 

. If you charge a balloon negatively, it can be stuck on a wall and it will remain in

place. Can the same thing be done with a positively charged balloon? Explain.

 

 

9. Two charges exert a certain force on one another. How is the force affected if the

magnitude of each charge triples?

10. How is the force between two charged particles affected when the distance between

the two charged particles is halved?

78

11.

12.

Two charges separated by one meter exert a 1 Newton force on one another. If the
charges are pushed to 0.5 m of separation, what will be the force that the particles
exert on each other now?

When do electrons flow in a wire?

 

13.
14.
15.
16.
17.
l8.
19.

What is the unit of electrical current?
What is the unit of electrical voltage?
What is the unit of electrical resistance?
What is the unit of electrical power?

 

Does current or voltage flow through a wire?
Does current or voltage get applied across a wire?

The current through a 2 ohm resistor connected to a 12-V power supply is what?

 

20.

A 5 ohm resistor has a 2 A current in it. What is the voltage across the resistor?

 

21.

22.

When a 9-V battery is connected to a resistor, 1 A of current flows in the resistor.

What is the resistor's value?
What is the electric power of a lamp that carries 3 A at 120 V?

 

23.

24.

A 60-W light bulb and a IOO-W light bulb are each rated at 120-V. Which light bulb
has the larger resistance?
What happens to the brightness of the bulbs as more lights are arranged in series?
Why?

 

 

25.

26.

27.

What happens to the current moving through the power source as more bulbs are
added to a circuit in series?
Does current flow through and then out a battery or does current simply flow out of

the battery?

 

How are the circuits in your car and house arranged: series or parallel? How do you

know?

 

79

28.

29.

30.

Two lamps, one with a thick filament and one with a thin filament are connected in
series. The current is greater in which lamp?
Two lamps, one with a thick filament and one with a thin filament are connected in
parallel to a battery. The voltage is greatest across which lamp?
Two lamps, one with a thick filament and one with a thin filament are connected in

parallel to a battery. The current is largest in which lamp?

 

Use the figure below to answer the following questions 31 - 36.

31 .
32.
33.
34.
35.
36.
37.

 

 

 

D E F 4
C

 

If each cell has a voltage of 1.5-V, what is the total voltage of the circuit?
How does the brightness of bulb C compare to Bulb E?
Bulbs A and B are connected in series or parallel?
Which group of bulbs draws the least current?
Which bulbs remain lit if bulb E is unscrewed?

At which numerical location would a fuse be located for this circuit?

When are batteries arranged in series?

 

 

 

 

 

38.

When are batteries arranged in parallel?

 

39.

What happens to the voltage as batteries are connected in series? In parallel?

 

80

40.

How does wire diameter relate to electrical resistance?

 

41.

If the resistance of a circuit is doubled, what happens to the current in the circuit?

 

42.

43.

If the voltage of a circuit is reduced to a quarter of its original value, what happens to
the current in the circuit?

What is meant when it is said that electric charge is conserved?

 

Two resistors connected in series have a certain resistance. The same two resistors
connected in parallel have a certain resistance. When connected in parallel, do the

resistors have more resistance, less resistance, or the same resistance?

 

 

45

. How does wire length relate to electrical resistance?

 

46

How does temperature relate to electrical resistance?

 

47.

How does the current in one location of a series circuit compare to the current in

another location of the series circuit?

 

48.

How do you determine the total amount of resistance in a series circuit?

 

 

49.

How does the sum of the voltage drops across each resistor in a series circuit relate to

the voltage of the source?

 

 

50.

How does the current in one location of a parallel circuit compare to the current in

another location of the parallel circuit?

 

81

51. How does the voltage drop across one pathway of a parallel circuit compare with the
voltage drop across a different pathway of the parallel circuit?

 

 

52. How does one determine the total amount of current in a parallel circuit?

 

53. What happens to the resistance of a parallel circuit as more branches are added to the

circuit?

 

 

 

54. Fuses blow and circuit breakers trip when there is a short circuit or when a circuit

becomes overloaded. Explain what happens in each circumstance.

 

 

 

 

 

 

55. Explain how to wire a household outlet.

 

 

 

56. Explain how to wire a household switch.

 

 

 

82

A-l7

 

Physical Science Name:
Electricity Unit
Electricity Pre and Post-Test Date: Hour:

 

 

Directions: Answer the following questions on a separate sheet of lined paper. Answer

each question fully in complete sentences.

1.

Explain why a balloon that has been rubbed against your hair can stick to a wall and
not fall off. Be specific.

. Two electrically charged objects brought near one another exert a force on each other.

Explain what two things affect the strength of this force.

. What is the difference between an insulator and a conductor of electricity? Give

examples of each.

. A ping-pong ball covered in aluminum foil is tied to a silk thread. A plastic comb is

rubbed with wool. When this happens, the comb becomes negatively charged. The
comb is then brought near the ping-pong ball until the two touch. The plastic comb is
then moved away from the ball and is rubbed with wool again. What will happen to
the ping-pong ball when the comb is brought near it? Explain why.

. What conditions are necessary in order to get electric charge to flow in a circuit?
. Explain the difference between current and voltage.
. What is the name of the units that are used to measure current, voltage, and resistance?

. Electrical resistance depends on many things. Explain how the amount of resistance

in a circuit depends on the length of the resistor and also how it depends on the
diameter of the resistor.

How do voltage and resistance affect the current in a circuit? For instance, what
happens if you double the voltage? Double the resistance?

10. Explain three differences between series and parallel circuits.

ll.

12.

A student sets up two different circuits. The first circuit is powered by two batteries
and has three light bulbs wired in series. The second circuit is powered by two
batteries and has three light bulbs wired in parallel. What happens to both circuits if
the middle light bulb is unscrewed?

A student sets up two different circuits. The first circuit is powered by two batteries
and has three light bulbs wired in series. The second circuit is powered by two
batteries and has three light bulbs wired in parallel. Are the bulbs in the series circuit
brighter, just as bright, or dimmer than the bulbs in the parallel circuit? Explain why.

83

13.

14.

15.

Are the fuses/circuit breakers in your house wired in series or in parallel? Explain
why this is the case.

Describe the relationship between the voltage of a battery and the voltage drop across
each resistance in a series circuit. Do the same thing for the resistors in a parallel
circuit. (Assume there is only one resistor in each branch of the parallel circuit)

Explain how current flows through a series circuit that is powered by a battery.
Specifically, explain whether current flows out of the battery and through the circuit
or through the battery and through the circuit. Also, explain whether the current is
the same at all places within the series circuit or if the current can vary at different
places along the circuit.

84

A-l8

 

Physical Science Name:
Electricity Unit
Electricity Multiple Choice Test Date: Hour:

 

 

Directions: Do not write on the test. X out the correct answer on your answer sheet.

I. The unit of electric charge, the coulomb, is the charge on _.
a. one electron b. a specific large number of electrons

2. The electric force between charges is strongest when the charges are _.
a. close together b. far apart c. the electric force is constant everywhere

3. The electrical forces between charges depends on the _.
a. magnitude of electrical charges
b. separation distance between electric charges
c. both of these
d. none of these

4. Rub electrons fi'om your hair with a comb and the comb becomes _.

a. negatively charged b. positively charged
5. An electron and a proton _.
a. attract each other b. repel each other
6. To say that an object is electrically polarized is to say _.
a. it is electrically charged b. its charges have been rearranged
c. it is only partly conducting d. it is to some degree magnetic
7. A balloon will stick to a wall if the balloon is charged _.
a. negatively b. positively

c. either (I. neither

8. Two charges exert a l-N force on each other. If the magnitude of each charge
doubles, the force will _.
a. be the same b. double c. quadruple
d. be eight times greater e. none of these

9. When the distance between two charges is halved, the electrical force between the
charges _.
a. quadruples b. doubles c. halves
d. is reduced to one quarter its original value c. none of these

10. Two charges separated by one meter exert a l-N force on each other. If the charges

are pushed to 0.25 m separation, the force on each charge will be _.
a. 1N b.2N c.4N d.8N e. 16N

85

11.

12.

I3.

14.

15.

l6.

17.

18.

19.

20.

21.

22.

A positive charge and a negative charge held near each other are released. As they
move, the force on each particle _.
a. increases b. decreases c. stays the same

An uncharged rice krispie grain is suspended by a silk thread flour a coat hanger.
When a negatively charged ebonite rod is brought nearby, without touching it, the

gram _.
a. becomes charged b. becomes polarized c. is repelled by the rod

Electrons are made to flow in a wire when there is _.
a. an imbalance of charges in the wire
b. a difference in the resistance between its ends
0. a voltage difference across its ends

An ampere is a unit of electrical _.

a. pressure b. current c. resistance d. power
Which statement is correct?
a. Current flows through a circuit b. Voltage flows through a circuit

c. Resistance is established across a circuit d. Current causes voltage

The current through a 10 ohm resistor connected to a 120-V power supply is _.
a. 1A b. 10 A c. 12 A d. 120 A e. none ofthese

A 10 ohm resistor has 5 A of current in it. What is the voltage across the resistor?
a.5V b. 10V c. 15V d. 20V e.50V

When a lO-V battery is connected to a resistor, 2 A of current flow in the resistor.
What is the resistor’s value?
a2!) b.5(2 c. 109 d.200 e.morethan2OQ

The electric power of a lamp that carries 2 A at 120 V is _.
a. 1/6W b. 2W c. 60W d. 120W e. 240W

In an electric circuit, the safety fuse is connected to the circuit in _.
a. series b. parallel

As more lamps are put into a series circuit, the overall current _.
a. increases b. decreases c. stays the same

A circuit is powered by a battery. Current flows _.
a. out the battery and into the circuit
b. from the negative battery terminal to the positive terminal
c. after a couple seconds pass
(1. through both the battery and the rest of the circuit

86

23. The headlights, radio, and defi'oster fan in an automobile are connected in _.
a. series b. parallel

24. Two lamps, one with a thick filament and the other with a thin filament, are
connected in series. The current is greater in the lamp with the _.
a. thick filament b. thin filament c. the same in each lamp

25. Two lamps, one with a thick filament and the other with a thin filament, are
connected in parallel to a battery. The voltage drop is greater across the lamp with
the _.

a. thick filament b. thin filament c. both voltages are the same

26. 24. Two lamps, one with a thick filament and the other with a thin filament, are
connected in parallel to a battery. The current is largest in the lamp with the _.
a. thick filament b. thin filament c. current is the same in both

27. A 60W light bulb and a 100W light bulb are each rated at 120 V. Which bulb has a
larger resistance?
a. the 60 W bulb b. the 100 W bulb c. both have the same resistance

Use the figure below to answer questions 28 — 33.

 

 

D E F 4
3 W
C

 

 

28. If each cell in the figure has a voltage of 1.5 volts, the total voltage of the circuit is

 

 

 

 

7: 1.5 V b. 3.0 v c. 4.5 V d. 6.0 v e. none oftlrese

29. How does the brightness of bulb A compare with the brightness of bulb D?
3. Bulb A is brighter
b. Bulb D is brighter
c. The brightness of each bulb is the same

87

30.

31.

32.

33.

34.

35.

36.

37.

38.

39.

Bulbs A and B are connected in _.
a. parallel b. series

Which bulb or group of bulbs draws the least amount of current?
a. BulbsA&B b. Bule c. Bulb D, E,&F

Which bulb or group of bulbs will remain lit if bulb A is unscrewed?
a.B,C,D,E,andF b. C,D,E,andF c. D,E,andF
d. C, E, & F e. C

At which location would a fuse be located for this circuit?
a. l b. 2 c. 3 d. 4 e. 5

An ohm is a measure of electrical _.
a. current b. power c. voltage d. resistance

Batteries are arranged in series when _.
a. a positive terminal from one battery is connected to the positive terminal of
another battery.
b. a positive terminal from one battery is connected to the negative terminal of
another battery.
c. a negative terminal fi'om one battery is connected to the negative terminal of
another battery.

How do wire diameter and resistance relate to one another?
a. The larger the diameter of the wire, the larger the resistance will be.
b. The smaller the diameter of the wire, the larger the resistance will be
c. Wire diameter and resistance do not relate to one another.

When four D-cell batteries are connected together in parallel, the total voltage of the
batteries is _. (Each D-cell is 1.5 V)
a. 1.5 V b. 3.0 V c. 4.5 V d. 6.0 V e. none of these

In a parallel circuit, _.
a. there is only one pathway for the voltage to move through.
b. there are multiple pathways for the voltage to move through.
c. there is only one pathway for the current to move through.
d. there are multiple pathways for the current to move through.

If the resistance of a circuit is quadrupled, the current in the circuit will _.
a. quadruple
b. be eight times greater than the original value
c. be sixteen times greater than the original value
d. be one fourth the original value
c. be one sixteenth the original value

88

40.

41.

42.

43.

45.

46.

Through which of the following methods can charge be transferred from one object
to another?
a. friction b. conduction c. polarization (1. all of these

As more bulbs are placed into a series circuit, they become dimmer and dimmer.
Why is this?

a. Since there are multiple pathways for the current to flow through, more bulbs
means more pathways. Each time an additional pathway is created, some of
the current is taken away from the other pathways. This makes the bulbs less
bright.

b. Each time a bulb is placed in series, the amount of voltage across the circuit
increases. The increase in voltage results in a decrease in current. This
decrease in current causes the bulbs to be less bright.

c. Each time a bulb is placed in series, the amount of resistance in the circuit
increases. As the amount of resistance increases, the amount of current
flowing through the circuit decreases. Less current means the bulbs will get
dimmer.

d. This does not happen. As more bulbs are placed into a series circuit, the
brightness of the bulbs remains unchanged.

If a negatively charged ebonite rod touches a rice krispie grain, the grain also
becomes negatively charged. If a different negatively charged rod is brought near
the grain, what happens?

a. nothing happens

b. the grain is attracted to the rod

c. the grain is repelled away fiom the rod

When the leaves of an electroscope are charged positively, they separate from one
another. What happens if a negatively charged rod is brought near the electroscope?
a. Since it does not touch the electroscope, nothing happens. The leaves stay the
same distance apart.
b. The closer the rod gets to the electroscope, the further the leaves separate from
one another.
c. The closer the rod gets to the electroscope, the closer the leave get to one
another.

When a charged comb is brought near a ping-pong ball, the ball is attracted to the
comb. By which method has the ping-pong ball been charged?
a. fiiction b. conduction c. polarization d. all of these

The opposition to the flow of current through a circuit is _.
a. voltage b. current c. resistance (1. power

For electricity to flow through a circuit, the circuit must be _.
a. in series b. in parallel c. open d. closed

89

47.

48.

49.

50.

To say that electric charge is conserved is to say that electric charge _.
a. may occur in an infinite variety of quantities
b. is a whole-number multiple of the charge of one electron
c. will interact with neighboring charges.
(I. can neither be created nor destroyed

A conductor differs from an insulator in that a conductor _.
a. has more electrons than protons
b. has more protons than electrons
c. has a higher resistance
d. has a lower resistance

If you plug a toaster rated at 110 V into a 220 V outlet, current in the toaster will be
about _.

a. half what it should be

b. the same as if it were plugged into 110 V

c. more than twice what it should be

d. twice what it should be

Compared to the equivalent resistance of two resistors connected in series, the
equivalent resistance of the same two resistors connected in parallel is _.
a. more b. less c. identical

90

APPENDICIES

Appendices B: Electricity Unit Teacher Resources

91

B-l

Electricity Unit
Teacher’s Guide for the Electrostatics Mini-Labs
8 total points - 1 point per question

Fill the Stockflrg

When the stocking is rubbed with the bag, the stocking becomes charged. Since the
entire stocking has become charged, and since like charges repel, the stocking “fills” up
magically as if a person’s leg was in it.

Electrostgtic Jumping Beans

When the cover is rubbed, it acquires a negative charge. This induces a charge in the
puffed rice and causes them to jump up to the cover. Once in contact, the puffed rice also
becomes negatively charged and is repelled away from the cover. Once they fall onto the
tin foil, they discharge and are ready to start the process over again.

Magcal Water

After the ebonite rod has been rubbed, it becomes negatively charged. When placed near
the water, it causes the polar water molecules to align themselves in the presence of the
rod’s electric field. The molecules align such that their positive side is facing the rod.
Since opposites attract, the water is pulled toward the rod. The same thing would happen
if the rod was positively charged.

The Obedient Ping-Pong Ball

When the negatively charged comb is brought near the ping-pong ball, it induces a charge
in the ping-pong ball. As long as the two don’t touch, you can get the ping-pong ball to
follow the comb.

The Dry Newspaper

After the newspaper has been rubbed, it acquires a charge. When the metal pie pan is
placed on the newspaper it acquires the same charge through contact. When the paper is
lifted off the table and a finger at a much different voltage is placed near the pie pan they
receive a shock.

The film Tree

Once the charged balloon touches the wire hanger, charge is transferred up the
conducting wire to the tissue. Since the tissue is now charged with like charges, the
individual strips now repel one another.

The Tricky Thr_e_q_d

After the comb has been rubbed, it becomes charged. As the rod is drawn up and away
fi'om the thread, a charge is induced in it and the thread will stand up when the comb is in
close proximity.

Mag’c Fingers
After you’ve acquired a charge, you can induce a charge in the pencil causing it to follow

your finger.
92

B-2

Electricity Unit
Teacher’s Guide for the Charged Grains Lab
9 points — 1 point per question

1.

After touchinLthe grin initi_ally. you opp not touch it again. The rognd the foil
covered grpin have the same charge. making them repel from one another.

. As the wool is brought p_e_ar the flip. the two obiects attract. They attract because

they hpve opposite charges.

. After touchingthe mp initially. you cap not touch it ggain. The rod and the foil

covered gflp have the same charge, making them reml from one another.

As the silkfiis brought near the gr_ain. the two obiects attract. They attract because
they hpve opposite charges.

. The two attract. The general conclu_sion that can be formed from this is that

oppositely charged objects are attracted to one another.

The two grg'ns are refilled away from one another. They hpve each gained the same
charge and objects with pfike chprge repel.

Alter touching one of the ggg'ns briefly. charge is removed fi'om that gr_ain. The other
gpain, however, is still charged. Consequently. the two gra__ip_s still repel, but now they
are closer to each other than they previoulewere. Obviou_sly. the amount of charge
on the grpins plays a role in the amount of force between them.

. If a known charge is placed on the gap, an unknown charge can be determined when

 

it is brorght neg the gr_ain. A like chgge will cplpse the ggrin to repel while the
opppsite charge will came the gg'n to attract.

 

The min bounces back and forth between the bglloonjs. Once it touches one balloorh
it apquires that charge and is repelled. It moves toward the other balloon which hfi
the opposite chgge beca_use opposites ma. Once it touches that balloon. it acquires
that charge and is repelled. The process continues in this fa_shion causing the gr_‘g'n to
bounce back and forth between themlloons.

 

93

B-3

Electricity Unit
Teacher’s Guide for Electroscope Lab
8 points - 1 point per question

1.

2.

The leaves sepa_r_ate from one gnother beczgse they hpvgained like charges.

The lepveshave become negatively chirged. We 153th the rod is negatively

charged and when it touches the foil ball some of this charge is tra_r__rsferred to the
leaygg of the electroscope.

 

 

. The lepves separate because a charge has been induced in them.

. As the charged 34 moves away, the leaves collapse bapk dpwn.
. IE differs fiom the previous example because in the previous example the leaves

stayed sepa_r_ated. This difference exifi beceppse in the second trial The leaves did not
pcquire aperm_anent charge.

. A charged rod needs to be placed near the foil ball of the electroscom without

touching it. A finger from the opposite hpnd then needs to touch the foil ball. The

finger gets removed, then finally the charged rod. A permanent charge has been left
on the electroscope without ever touching it with the rod.

 

. The leaves have acquired g positive charge. One knows thljgrecause the negatively

charged rod will cause the leaves to collapse.

. A msitively charged object would cause the leaves to mm further, a negatively

charged obiect would cargo the lepves to collapse.

94

B-4

Electricity Unit
Teacher’s Guide for Electrophorus and Leyden Jar Lab
7 points - 1 point per question

1.

2.

You receive a pretty good shock.

The pie pan has a large positive charge. This is apparent because when it is brougm
near the negatively charged electroscom, the leaves collapse.

 

 

 

 

. It would seem that the pie pan would be nggativeLy charged because the electrophorus

was negativelv charged. This is not tthaae. however. Instead, the pie pan becomes
positively grarged becaase the pan sits on top of ridges in the record. Since it is not in
mm with the maioritv of the record. the electrophogs induces a charge in the pie
pan. The positive charges shift toward the bottom of the pan__ while the negative

charges shift toward the top of the m. When the pie pan is touched, the some of the
negative charge is drained away by the finger, leaving the pan positively charged.

 

When the pie pan is brought nea; the circuit tester. it flashes with light indicating that
there was a difference in voltage between the two terminals of the tester.

. A large spark forms.

. This flash of light is brighter gap before.
. The concluaion that can be drawn from this is that the Leyden Jar storea electric

 

charge. Therefore. there is a ggeater voltage difference between the two terminals of
the tester causing the flash of light to be brighter.

 

95

B-5

Electricity Unit
Teacher’s Guide for Flowing Water Mini-Lab
3 points (1 point per question)

1. The water stops flowing when the height of the water is the sag: in the two
containers.

2. The exact same thing hapmns. Even though the containers have a different diameter
yvater flowa out of one confirm fl] into the other u_ntil the lgight of the water is thg
same in each. -

 

3. In order to get water to flow. there need_s__ to be a pressure difference. This means that
the water levelfiat one location mu_st be higher than the water level at a different
location. As long as this difference existsgvater flowa. Once the water levels even

out, water stops flowing.

96

B-6

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Electricity Unit
Teachers Guide for the Current Lab
9 points (1/2 point for each row in the table, 4 points for the conclusion)
Current Detected Amount of Needle
(yes or no) Deflection (°)
Zinc and copper No
Zinc and copper connected in No
a complete circuit
Zinc and copper in distilled No
water
Zinc and copper in tap water Yes *
Zinc and copper in salt water Yes "*
Zinc to copper to zinc to Yes "***
copper in salt water
Zinc and copper separated by Yes **
salt water soaked felt
Copper and copper in salt No
water
Zinc and zinc in salt water No
Zinc and copper in sugar No
water
Zinc and copper in apple Yes **
Conclusion

Electric current is created when there is a potential difference between two electrodes that
are separated by an electrolyte. A potential difference exists between copper and zinc but
not between copper and copper or zinc and zinc.

A current can be drawn when zinc and copper electrodes are placed into any solution that
is an electrolyte.

More current is drawn when zinc and copper cells are connected in series. Enough cells
can run small electrical devices like a wall clock.

97

 

Electricity Unit

Teachers Guide for Resistance Lab

B-7

13 points (1 point each for the questions, 5 points for the table, 4 points for the graph)

1. What happens to the flashlight bulb as the two alligator clips move away from one

another?

As the alligator clips move away fi'om one another, the light bulb ggows dimmer.

 

 

 

 

 

 

 

Sample Data
Play-Doh Voltage (V) Current (mA) Current (A) Resistance
Diameter (cm) (Q)
1.15 1.33 6 .006 222
1.5 1.36 9 .009 151
1.9 1.20 12 .012 100
2.2 1.30 15 .015 86.7

 

 

 

 

 

Resistance vs. Diameter of Play-Doh "Wires" at a Constant Voltage

250

§ §

Resistance (ohms)
§

 

 

 

 

0.5

 

 

 

 

1 1.5

Diameter (cm)

98

__+~

 

2.5

 

2. How does the length of a resistor affect the current of a circuit? Explain how you
know this and explain why this occurs. (Reflect on Part A)
As the length of a resistor increases. the amount of current present in a circuit decreases.

This is evident because as the alligator clip was slid down th_e pencil lead. the light bulb

 

ggew dimmer. The bulb is dimmer because of the increased resistance. Hence. fewer
charges move by the filament every second causing the bulb inten_sity to decrease.

3. What mathematical relationship between resistor diameter and resistance does the
graph illustrate?
It is evident that as the diameter of the resiator increases. the resistance of that resistor

decreases. In fact. the two are inversely proportional.

4. Briefly summarize the findings of this lab. Specifically, how does the resistor length
and the resistor diameter affect the resistance and the current in a circuit.

This lab has shown that as the length and resistance are directly promrtional while
aiameter and resistance are inversely proportional. Therefore. the lergth of msistor i§

 

inversely proportional to carrent while the diameter of fleshstor is directly promrtional
to current. Therefore. if one wants the naaximum amount of cu_rrent fiom yesiator. he
ahould make the resistor’s diafimeter large while making its length short.

99

Electricity Unit

B-8

Teacher’s Guide for the Cells in Series and Parallel Lab
15 points (1 point per question, 8 points for the two graphs)

 

 

 

 

 

 

 

 

 

 

Cells in Series Cells in Parallel
# of cells voltage (v) # of cells voltage (v)
1 .721 1 .721
2 1.45 2 .734
3 2.18 3 .725
Voltage vs. Number of Cells Wired in Series
y = 0.7295x - 0.0087
2.5

1 .5
Voltage

0.5

 

Number of Cells

100

 

Voltage vs. Number of Cells Wired in Parallel
= 0.002x + 0.7227

 

0 0.5 1 1.5 2 2.5 3 3.5
Number of Cells in Parallel

1. How does the number of cells connected in series affect the voltage of the system?

The more cells there are, the higher the voltage is. Whe_n the cellwe 1.5 Vaeaah
additional cell will add an additional 1.5 V to th_e circuit.

 

2. How does the number of cells connected in parallel affect the voltage of the system?
No matter how many cells are connected in parallel, the voltage of th_e circuit is always

the same.

3. What is an advantage of adding cells in series?

The advantage of adding cell§ in series is that the voltage of the circuit i§ increaaea,
While we haven’t studied this yet. it will later become apaarent that voltage and current
are directly promrtional. Therefore. the garter the voltage of a circuit. the ggeater the

current of tha; circuit.

4. A remote control car requires 12 volts to operate. How many 1.5 volt batteries would
be necessary to power the car? How must the batteries be arranged?
Qae would need to arrange 8 batteriea in series to obtain the 12 volta required.

101

5. How do you think the addition of cells in parallel affects the longevity of these cells?
Will they last for a longer time or a shorter time? Why do you think this?

Adding cells in parallel does not affect 6154on of the circuit. Therefore a circuit
_runn_ing off of 1 battery or 5 batteries in parallel will have the same voltag_e__and hence the
_asame amount of current. If they each have the same current. than_the circuit with 5
batterieghould last for much longer becaase only pmme current is passing through

each batteg. Therefore, fewer electrons are passing through each battery per unit time.

thus extending the life of the battery.

 

102

B-9

Electricity Unit
Teacher’s Guide for Circuits in Series and Parallel Lab
(10 Points — 1 point per question)

All diagrams must show the tip of the light bulb and the side of the light bulb connected
in some way to the positive and negative terminal of the battery to receive credit for the
drawings.

1. Describe the similarities among your successful trials.
All successful trials must have a complete circuit. The side of the metallic base and

bottom of the metallic base mu_st be connacted to the poaitive and negative terminals of
the batteg. Ifthese conditions are not met, the bulb will not light.

 

2. What two parts of the bulb does the holder make contact with?
The side of th_e metflic base and the bottom of the metallic base.

3. Do the bulbs light in each of the series circuits you have designed?
If connected promrly, yes.

 

4. Which circuit contains the brightest bulb or bulbs? The dirnmest bulb or bulbs? The
first, second, or third?
Brightest = 1 bulb which was the first circuit. Dirnmest = 3 bulbs in series which vyas the

third circuit.

5. What happens when a bulb that is connected in series is unscrewed from its base?
All th_a bulba in the circuit go out. Current has only one pathway to follow anal when that

pathway is brokea electrons can no longar move.

 

 

 

6. Do the bulbs light in each of the parallel circuits you have designed?
If connected promly, yes.

 

7. Which parallel circuit contains the brightest bulb or bulbs? The dirnmest bulb or
bulbs?
All circuits are a entl the same bri tness.

103

8. What happens when a bulb that is connected in parallel is unscrewed from its base?

_Th_at bulb will go out; however. the othar bulbs in the circuit remain lit.

9. Summarize the differences between series and parallel circuits.
In a series circuit, there is only one pathway for electron flow. Therefore. as more
resistances are added to the circuit. current decrefies. Also, if thgathway is broken at

any ppinh all devicea stop working. In a parallel circuit. there are multiple pathways for
electrona to follow. Each resistance is connected to the msitive and negative terminal of

 

the battery; therefore. the voltaggcross each resigance is identical. Con_sequently. the

current for each resistance will be the same (assuming the resistors all have the same
resistance). Since there are multiple branches connected to the battegy terminals, if one

device a removed. the othera MlLsfill wcak.

104

Electricity Unit

Teacher’s Guide to Ohm’s Law Lab

25 points (Tables — 5 points, Graphs -14 points, Questions 1 point each)

B-lO

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

# of Batteries Current (mA) Current (A) Voltage (V)
1 4.54 .00454 1.50
2 9.4 .0094 3
3 13.72 .01372 4.54
4 18.38 .01838 6.07
Resistance (0) Voltage (V) Current (mA) Current (A)
33 All 84.5 .0845
39 Around 72.2 .0722
47 3.0 60.5 .0605
51 55.6 .0556
100 29.58 .02958
150 19.93 .01993
180 16.45 .01645
330 9.19 .00919
470 6.44 .00644
560 5.4 .0054
820 3.69 .00369
1000 3.06 .00306
3900 .77 .00077

 

 

 

 

105

 

 

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106

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y = 2.7939x + 0.0006

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1/Resistance (l/ohms)

1. What mathematical relationship between voltage and current does the graph illustrate?

Voltage and Current aae directly proportionah

2. What mathematical relationship between resistance and current do the graphs
illustrate?

Resistance and current are inversely propprtional.

 

3. What does the slope of the voltage vs. current graph represent? How closely does it
agree with the actual value? (Calculate the % error)
It represents the resistance of the resistor that was used during part A. The slope of the

 

line I obtained waa333 £1. The actual value of the resistor was 3303. The percent
difference i§ 0.91%.

4. If a fifth D-Cell battery was added to the circuit for part A, what would you expect the
current to be for the circuit? Why?
I would expect the current to be roaghly .0229 A.

5. What does the slope of the current vs. 'lmismoc graph represent? How closely does it
agree with the actual value? (Calculate the % error)
It represents the voltage that was used during Part B. The slope of the line I obtained wg

2.80 V. The actual measured voltage was 3.01 V. The percent differenccm 6.98%.
107

6. Did the potential difference across the resistor in part B change when you changed the
resistor in the circuit?
The potential difference did not change. The resistors were always connectedaxoss the

same two D-Cells. Therefore. the voltage didn’t change.

108

B-ll

Electricity Unit
Teacher’s Guide for the Ohm’s Law with Series Circuits Lab
16 points (1 point per question)

Current (I) = .02958 A Voltage (V) = 2.922 V Calculated Resistance R1 = 98.78 I)

1. How does the calculated value of the resistance compare to the manufacture’s rated
value? Calculate the % error.

Calculated Value is 98.780. Actual Value i§ 1009a. % differe_nce is 1.22%.

Current at A1 = .01082 A Current at A2 = .01082 A Current at A3 = .01082 A
Voltage V. = 1.071 V Voltage V2 = 1.921 V Voltage V3 = 2.990 V

4. How do the current readings compare?

The current readings are identical.

5. How do the three voltage readings compare?
The voltages across the two resistors vary. The voltage across the smaller reaistor is
_s_n_raller than the voltage across the larger res_istor. The sum of the voltages is equal to the

voltagg of the sou_rce.

6. Calculate the values of R1 and R2. Show your work.
Ry= 98.98Q R; = 177.54 Q

7. Divide V3 by the current. How does the result compare to the sum of the resistances
you calculated in part 6?

276.34 a Thia_ia very close to the sugn of the resistances from part 6 - 276.525;

8. What is the relationship among the current in the circuit, the sat; of the resistances,
and the voltage across all the resistances?
I = Vl/Rgg = 2.990/276.52 = .010813 A

This means that the m current for a series circuit is canal to the awn of the voltges

across each resistance divided by the sum of the resistors in the circuit.

109

R1=10 Q R2=l8 Q R3=2]_QQ

V4 = .02 V

9. According to the manufacturer’s ratings, what is the total resistance in the circuit?
The total resistance is 5503!;

10. Predict what the readings will be for the multimeters measuring current at A1, A2,
and A3.
I = V = 302/550 = .00549 A.

Current at A1 = .00555 A Current at A2 = .00555 A Current at A3 = .00555 A
Voltage VI = $9 V Voltage V2 = 3% V Voltage V3 = 1.477 V

11. How do your measured values of the currents through the multimeter compare to the
value you predicted in step 4?
They are vegy close (1.08 % off)

12. Calculate the values of the resistances of R1, R2, and R3 from your current and
voltage measurements. Show your work.
R1 = 99.1 (2L R2 = 177.66g R3 = 266.130

13. Divide V4 by the current. How does the result compare to the sum of the resistances
you calculated in part 12?

544.14g This is vegy close to the sum of the calculated resistances from above
(542.899).

 

 

14. How do the currents in different parts of a series circuit compare?

The current in all parts of a seriea circuiflre identical.

15. Describe the relationship among the voltage of the source and the voltages across
each resistance in a series circuit.

The sum of the voltages across all resistors in a series caa' uit is agual to the voltage
across the source. Moreover. the voltages across large resistors are higher than the

voltages across small resistors.

 

 

16. Describe how current relates to the sum of the resistances and the sum of the
voltages.
Current = The sum of the voltages divided by the sum of the resistances in a series

circuit.

110

B-12

Electricity Unit
Teachers Guide for Ohm’s Law with Parallel Circuits
15 points (1 point for each question)

Current (I) = .0293 A Voltage (V) = LEE V Calculated Resistance R1 = 100.68 (2

1. Predict whether the current measured at A3 will be greater than, less than, or the same
as the current measured in step 1.

It sh_ould be gr_eater. There are multiple pathways each receiving the voltage of the
aource. Conaequentlyacurrent should be ggeater.

2. Predict whether the voltage V; across the first resistor will be greater than, less than,
or the same as it was in step 1.

The voltage should be the same ask it waa in step 1. All branches of the circuit sthould

 

have the same voltage.

Current at A r = A Current at A2 = A Current at A3 = A
Voltage V1 = V Voltage V2 = V Voltage V3 = V

3. How do the three current readings compare?

I do nothave this information. but the current ahould be the same for A] and A2. It
flould be the same because the voltage is the same and the resistors are of equal value.
However. A3fs_hould be the smn of A 1 + Al. The current through the circuit will be the
sum of the current through each pathway.

 

4. How do the three voltage readings compare?
They should be identiaal to one another. Each pathvary is connected to the aositive and
negativeflttery terminal ', therefore, they should all have the same voltage.

5. Calculate the values of resistances R1 and R2 using Ohm’s law. Show your work.
I do not do have this informatiop, but R] and R2 should come out to be the same.

111

6. Calculate the equivalent resistance of the circuit by dividing the voltage of the source,
V3, by the current through the source, A3. Show your work.
I did not do this. but the equivalent resistance should be less than either resistor. The

flson for this is the voltage_across each resistor is identical. Therefore. the more
pathways there are. the higher the current is going to be. Ohm’s law states that current
and resistance are inversely proportional. So. as the current increases throagh the circuit.

the resisaarrce of the circuit has to lower.

7. How does the equivalent resistance of the circuit compare with the two values you
calculated for the individual resistances in number 5.
See answer for #6.

Current at A1 = .0293 A Current at A2 = .01648 A Current at A3 = .0450 A
Voltage V1 = E; V Voltage V2 = A2; V Voltage V3 = M V

8. How do the three current readings compare?
The current differs through the two branches because the value of the resiator varies. The

sum of the two currents thou is the total current of th_e circuit. Al + A; = A3.

9. How do the three voltage readings compare?
The voltages are close to identical.

10. Calculate the values of resistances R1 and R2 using Ohm’s law. Show your work.
R1 = 100.68 Q R; = 179.00g.

11. Calculate the equivalent resistance of the circuit by dividing the voltage of the

source, V3, by the current through the source, A3. Show your work.

$566.69:

12. How does the equivalent resistance of the circuit compare with the two values you
calculated for the individual resistances in number 5.

The muivalent resistaaze is less than either of the resistors in part 5.

112

13. Describe the relationship among the currents in a parallel circuit.
The sum of the currents through each branch is equal to the tota current of the circuit.

14. Describe the relationship among the voltages in parallel branches of a circuit.
All the voltages in the circuit are identical.

15. Describe the relationship among the equivalent resistance and the individual
resistances in a parallel circuit.

The equivalent resistance i§ less than the mllest resis_t_ance in the circuit. For an

explanation why this i§. see number 6.

113

B-13

Electricity Unit
Teacher’s Guide for the Fuses Lab
7 points (1 point per question)

1. What happens when the switch is closed?

Thasteel wool melts. thu_s opening the circuit.

2. What happens when the switch is closed initially?
The bulb lights and remains lit.

 

3. What happens when the two bare sections of wire are touched together? Why does
this happen?

The steel wool melta. When the bare sectionaare touched together, a low resistance

pathway is creafl that allows current to bypass the light. Since currept increases
dramatically. the fu_se melts, the circuit opens, and the light bulb is no longgr lit.

 

 

4. How many bulbs were required to melt the firse?
Answers will vary demnding on the size of the steel wool fu_aa.

5. Why doesn’t the fuse blow initially? Why do you have to add more bulbs to get the
fuse to blow?

The fuse does not blow initially because there is not enopgh heat to melt the steel wool.
As more bulbs are added in Mlel, the guivalent resistance of the circuit decreases

causing the current of the circuit to increase. Eventually it increases enou to melt the

 

 

steel wool.

6. The firse boxes of some older houses were not designed to carry the loads required by
modern appliances. To avoid continuously replacing fuses, some people replaced
fuses with copper pennies. Explain why this is extremely dangerous.

This defeats the pamse of having a fuse. If a circuit is aborted or overlaaded. wires ca
become overheated aad potentially start a fire. The problem with the penny is that it is
not going to melt in time to prevent a fire. It would take way too much amp_erage to melt

the penny.

114

7. Why are fuses connected in series with the power supply while all the other appliances
are connected in parallel?

 

Fuses are connected in series because evepm'ng in a series circuit stops wo king when
the circuit is opened. Con_sequently. when the fuse melts. the circuit is broken and all
appaances star wrakang. If it was connected in paaallel. the other appliances would still
worlaeven after the fuse blows. This would defeat the purpose of the fu_se.

8. The amperage rating for a fuse is stamped onto the fuse. The car firse shown in the
first picture is rated at 15 amps. This means that a current of 15 amps can pass
through the fuse, but any additional current will cause the wire in the fuse to melt.
Explain how you could determine the amperage rating for your steel wool strand and
actually measure it if time permits.

One could hoolaa multimeter up in series with the fi.1_se. Sha could then add additional
lamps noting the current running through the circuit. Sh_e would continue adding lamps
until the fuse blew. The current reamg on the multimeta prior to the fuae blowing
wouldaive her the ammage rating (roughly) of the steel wool fu_se.

 

115

B-14

Electricity Unit
Teacher’s Guide for Household Wiring Lab
(20 Points — all or nothing for hooking up the circuit correctly)

Students must hook the circuit up as follows:

2 outlets

Black wires to brass side push-in fittings

White wires to silver side push-in fittings

Bare copper wires pig tailed and attached to the green grounding screw

Switch

Black wires to push in fittings in the back

White wires wire nutted together

Bare copper wires pig tailed and attached to the green grounding screw

Light Fixture

Black wire attached to brass screw on fixture

White wire attached to silver screw on fixture

Bare copper wire attached to green grounding screw in electrical box

Outlets tested with a receptacle tester. If the two yellow lights come on, the outlet is
wired correctly.

Fixture is tested by turning on the switch. If the outlets are properly wired and the light .

comes on, students get the full 20 points. If not, students must find their mistake and fix
it.

116

B-15
Electricity Unit
Teacher’s Guide for the Cost of Electricity Activity
10 points (1 point for rate charged, 1 point each for power rating, energy consumed, and

cost to use device for the month)

1 point for rate charged — should be between 5 — 10 0: per kWh.

1 point for each of the three power ratings — checked against power rating tables obtained
from the internet to make sure they are in the correct range.

1 point for each of the three energy consumed calculations (power rating times time used
per month)

1 point for each of the three cost to use device for the month calculations (energy
consumed times rate power company charges)

117

B-16

Electricity Unit
Teacher’s Guide for the Electricity Study Guide
(No Points -— Students get answer sheet if the complete study guide)

1.

2.
3

8.

9.
10.
11.

12.
13.
14.
15.
l6.
17.
18.
19.
20.
21.
22.
23.

24.

25.

26.

The unit of charge is the Coulomb. It represents the charge of billions and billions of
electrons.
The magnitude of the two charges and the distance the two charges are separated.

. The closer they are to on another, the greater the force is between them. The further

they are moved apart, the weaker the force is between them.

. electron = negative, proton = positive, As the particles are brought near one another,

they are attracted to each other. Opposite charges attract.

. friction, conduction, induction or polarization
. friction, comb becomes negatively charged and hair becomes positively charged (hair

strips electrons off the balloon)

. Electrical polarization means the charges in an object have been rearranged giving one

side of the object a slight positive charge and the other side of the object a slight
negative charge. The object, overall, is still neutral.
Yes, a positively charged balloon will induce a charge on the wall and allow it to stick
just like a negatively charged balloon would.
Use your formula -—> 3 3/12 = 9. This means the force will be nine times greater.
1 l/( /2)2 = l—lm — 4. This means the force will be four times greater.
This question uses information from number 11. You need to see that the distance of
the particle separation goes from 1 meter to half a meter. Since the distance is
halved, the force quadruples. The original force was 1 N so the final force will be 5
Newtons.
They flow when there is a voltage difference across the ends of the wire.
The ampere
The volt
The ohm
The watt
Current flows through a wire.
Voltage is applied across a wire.
I=V/R=12V/2ohms=6amps
V=l~R=2A-50hms=10volts
R=V/I=9V/1A=9ohms
P=I~V=3A~120V=360Watts
The 60 Watt light bulb has a larger resistance because it is drawing a smaller current.
If the current is less, that means there must be more resistance preventing the current
from being higher.
The bulbs grow dimmer and dimmer. Each time a bulb gets added the voltage gets
divided up more. Since there is less voltage per light bulb, the current decreases
causing the light bulbs to dim.
The more bulbs there are, the less bright the bulbs are. The dimmer bulbs prove that
the current in the circuit has decreased. Since the current has to be the same through
all parts of the circuit, the current through the power source must decrease as well.
Current flows through the battery and the rest of the circuit.

118

27.

28.

29.

30.

31.
32.

33.
34.
35.
36.

37.

38.

39.
40.
41 .
42.
43.

45.
46.
47.
48.

49.

50.

Circuits in your home and car are arranged in parallel. If they were not, as soon as
one appliance was turned off, all the others would shut off as well.

The current in every portion of a series circuit must be identical. Therefore, the
current through each light is the same. The reason why the current must be the same
for all portions of a series circuit is because there is only one pathway through which
the current can move.

The voltage is the same across both lamps. Lamps connected in parallel are
connected so that all lamps are connected to the same two battery terminals. Since
they are connected to the same terminals, they have the same voltage.

Since there are multiple pathways through which current can flow in a parallel
circuit, there can be different currents in different pathways. The two bulbs are
connected so that they have the same voltage. Therefore, the current will be greater
through the light bulb that has less resistance. Thick wires have less resistance than
thin wires; therefore, the current will be larger through the bulb with the thick
filament.

3.0-V because there are two 1.5-V batteries.

Bulb C is dimmer than bulb G. (More bulbs in series = less current. Less current =
dimmer bulbs)

Series

B, C, D, and B because they are the dirnmest. Dimmer bulbs mean less current.

A, F, and G remain lit.

At location 1. If it was located anywhere else, it would not be effective. When it
blows at location 1, every other light bulb would go off. If it was located anywhere
else, it would only shut off a portion of the lights.

Batteries are in series when the positive terminal of one battery is connected to the
negative terminal of another battery.

Batteries are in parallel when the positive terminal of one battery is connected to the
positive terminal of another battery.

In series, voltages get added together. In parallel, voltages do not add together.

As wire diameter increases, resistance decreases.

Current is cut in 1/2.

The current is reduced to 1/4 its original value.

Charge can neither be created nor destroyed, simply transferred fi'om one location to
another.

In parallel, the resistors have less resistance. Think of bulbs in series and parallel.
Two bulbs in series are dimmer than two bulbs in parallel. Therefore, the bulbs in
parallel must have a larger current. That means the resistance must be lower.

As the length of a wire increases, resistance increases.

As the temperature of a conductor increases, resistance increases.

The current at all locations of a series circuit is the same.

Add each individual resistor up. If you have a 20 Q, 80 Q, and 100 Q resistor, the
total amount of resistance in the circuit is 200 Q.

The sum of the voltage drops across the resistors in a series circuit is equal to the
voltage of the source. Therefore, if you have a 9.0 V source, the voltage drops across
the various resistors in the circuit need to add up to 9.0 V. If you have two resistors
and the voltage drop across one resistor is 4 V, the voltage drop across the other
resistor would need to be 5 V.

The current running through different branches of a parallel circuit can be different.

119

51.

52.

53.

54.

55.

56.

The voltage drop across each pathway of a parallel circuit is the same. If you have a
9.0 V source, then the voltage drop across each pathway will be 9.0 V. The voltage
drop will be the same as the source's voltage because each pathway is connected to
the positive and negative terminal of the battery.

The total current in a parallel circuit is equal to the sum of the currents in the
branches.

As more branches are added, the amount of resistance in the circuit decreases. Just
like if more checkout lines are opened at a supermarket, the amount of "congestion"
in the supermarket decreases.

During a short circuit, wires on opposite sides of an appliance touch. This creates a
low resistance pathway that allows current to bypass the appliance. Current
increases dramatically during a short circuit and can cause a fuse to "blow" or a
circuit breaker to "trip". As additional branches are added to a parallel circuit, the
overall resistance of the circuit decreases. A decrease in resistance creates an
increase in current. The higher current causes the wires to heat up and can cause a
fuse to "blow" or a circuit breaker to "trip". This situation occurs when the circuit
becomes overloaded.

To wire a household outlet, connect the black wires to the brass screws, the white
wires to the silver screws, and connect the ground wires together and to the green
grounding screw.

To wire a household switch, connect the black wires to the brass screws, connect the
white wires together in a wire nut, and connect the ground wires together and to the
green grounding screw.

120

B-l7

Electricity Unit
Teacher’s Guide for Short Answer Electricity Test
105 Points (Test worth 35 points — multiplied by 3)

The following items needed to be included in the answer to receive points

1. 3 points
0 Balloon becomes negatively charged because it takes electrons off your hair
0 Balloon placed near a wall induces a charge in the wall such that the positive
centers of charge have shifted toward the surface of the wall
0 Opposites attract causing the balloon to move toward the wall and stick to it

2. 2 points
I The force is directly proportional the product of the two charges
0 The force is inversely proportional to the square of the separation distance

3. 3 points
0 Insulators are materials that do not contain movable electric charges and have
high electrical resistances. A conductor is a material that contains movable
electric charges and has low electrical resistances.
Conductors are typically made out of metals, like copper, silver, and gold
Insulators are typically nonmetals, like air, wood, and rubber

4. 2 points
0 The ping-pong ball will be repelled as the negatively charged comb is brought
near it.

o The two will repel because each is negatively charged. Like charges exert a
repulsive force on one another.

5. 2 points
0 One condition necessary to get electric charge to flow in a circuit is a complete
circuit without any breaks or gaps.

o A second condition necessary to get electric charge to flow is a voltage difference
across the circuit. One obtains a voltage difference from a power source such as
batteries, an electrical outlet, or a generator.

6. 2 points
0 Current is the flow of electric charge through a circuit and is defined as the
amount of charge that passes through some portion of a circuit in a given amount
of time.
0 Voltage is the electrical pressure that is applied across a circuit and is necessary to
get a current to flow. Voltage is defined as potential energy per unit charge.

121

7. 3 points
0 Current is measured in amps
0 Voltage is measured in volts
0 Resistance is measured in ohms

8. 2 points
0 As the length of a resistor increases, the amount of resistance in the circuit also
increases. The two are directly related.
0 As the diameter of a resistor increases, the amount of resistance in the circuit
decreases. The two are inversely related.

9. 3 points

0 Voltage and current are directly proportional. Therefore, as voltage increases so
does current. Resistance and cm'rent are inversely proportional. Therefore, as
resistance increases, current decreases.

o If the voltage across a circuit is doubled, the amount of current flowing through
the circuit will also double.

0 If the resistance across a circuit is doubled, the amount of current flowing through
the circuit will be cut in half.

10. 3 Points

0 A series circuit contains a single pathway for current to move through, a parallel
circuit contains multiple pathways.

0 The current flowing through a series circuit is the same at each location in the
circuit. A parallel circuit may have different amounts of current flowing through
different branches.

0 The sum of the voltage drops across the resistors in a series circuit is equal to the
voltage of the power source. The voltage drops across the branches of a parallel
circuit is equal to the voltage of the power source.

0 Other answers could also be accepted here.

11. 2 Points
0 If the middle bulb of a series circuit goes out, all of the bulbs in the circuit will go
out. Since there is only one pathway for electric charges to flow through, a break
anywhere in the circuit causes current to stop flowing.
o If the middle bulb of a parallel circuit goes out, all of the other lights will remain
on. Since there are multiple pathways for current to flow through, only the
pathway that has been opened will stop working.

12. 2 Points

0 The bulbs in the series circuit are dimmer.

I The equivalent resistance of a series circuit can be determined by adding together
the resistors. The more resistors in a circuit, the greater the amount of resistance
in a circuit. Since resistance and current are inversely proportional, more
resistance means less current. Consequently, the lights are dimmer. The
equivalent resistance of a parallel circuit is less than the individual resistors
because more pathways decrease the total amount of resistance.

122

B-18

Electricity Unit
Teacher’s Guide for the Multiple Choice Electricity Test
100 points (Test worth 50 points — Multiplied by 2)

Answers

1. B 26. A
2. A 27. A
3. C 28. B
4. A 29. A
5. A 30. B
6. B 31. C
7. C 32. B
8. C 33. A
9. A 34. D
10. E 35. B
11. A 36. B
12. B 37. A
13. C 38. D
14. B 39. D
15. A 40. D
16. C 41. C
17. E 42. C
18. B 43. C
19. E 44. C
20. A 45. E
21. B 46. D
22. D 47. D
23. B 48. D
24. C 49. D
25. C 50. B

124

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126

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