Download Current Electricity guide

Current
Electricity
Teacher’s Guide
Grades 5-9
Produced by:
Brian A. Jerome, Ph.D.
Stephanie Zak Jerome
Narrated by:
Nina Keck
Production Assistant:
Jessica Kassis
Visual Learning Company
Brandon, Vermont
1-800-453-8481
www.visuallearningco.com
Current Electricity
Contributors and
Reviewers:
Producers:
Brian A. Jerome, Ph.D.
Stephanie Zak Jerome, MPA
Reviewer:
Metin Yersel, Ph.D.
Lyndon State College
Lyndon, Vermont
Narrator:
Nina Keck
Graphics:
Meredith Patch
Use and Copyright:
The purchase of this video program entitles the user the right to reproduce or
duplicate, in whole or in part, this teacher’s guide and the blackline master
handouts for the purpose of teaching in conjunction with this video, Current
Electricity. The right is restricted only for use with this video program. Any
reproduction or duplication, in whole or in part, of this guide and student
masters for any purpose other than for use with this video program is
prohibited.
The video and this teacher’s guide are the exclusive property of
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from the copyright holder is prohibited (Title 17, U.S. Code
Sections 501 and 506).
082100
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Current Electricity
Table of
Contents
Page
A Message From Our Company
5
National Standards Correlations
6
Student Learning Objectives
7
Assessment
8
Introducing the Video
9
Video Viewing Suggestions
9
Video Script
11
Answers to Student Assessments
16
Answers to Student Activities
17
Assessment and Student Activities Masters
18
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Current Electricity
Viewing
Clearances
The video and accompanying teacher’s guide are for
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library settings, or similar instructional settings.
Duplication rights are available, but must be negotiated with
the Visual Learning Company.
Television, cable or satellite rights are also available, but
must be negotiated with the Visual Learning Company.
Closed circuit rights are available and are defined as the use
of the program beyond a single classroom but within a single
campus. Institutions wishing to utilize the program in
multiple campuses must purchase the multiple campus version
of the program, available at a slightly higher fee.
Discounts may be granted to institutions interested in
purchasing programs in large quantities. These discounts may
be negotiated with the Visual Learning Company.
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Current Electricity
A Message from
our Company . . .
Dear Educator:
Thank you for your interest in the educational videos produced by the
Visual Learning Company. We are a Vermont-based, family owned and
operated business specializing in the production of quality educational
science videos and materials.
We have a long family tradition of education. Our grandmothers graduated
from normal school in the 1920’s to become teachers. Brian’s mother was an
elementary teacher and guidance counselor, and his father was a high school
teacher and superintendent. This family tradition inspired Brian to become a
science teacher, and to earn a Ph.D. in education, and lead Stephanie to work
on science education programs at NASA.
In developing this video, accompanying teacher’s guide, and student
activities, our goal is to provide educators with the highest quality materials,
thus enabling students to be successful. In this era of more demanding
standards and assessment requirements, supplementary materials need to be
curricular and standards based - this is what we do!
Our videos and accompanying materials focus on the key concepts and
vocabulary required by national and state standards and goals. It is our
mission to help students meet these goals and standards, while experiencing
the joy and thrill of science.
Sincerely,
Brian and Stephanie Jerome
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Current Electricity
National Standards
Correlations
National Science Education Standards
(Content Standards: 5-8, National Academy of Sciences, c. 1996)
Science as Inquiry - Content Standard A:
As a result of activities in grades 5-8, all students should develop:
• Abilities necessary to do scientific inquiry
• Understandings about scientific inquiry
Physical Science - Content Standard B:
As a result of their activities in grades 5-8, all students should develop
an understanding of:
• Transfer of Energy
Benchmarks for Science Literacy
(Project 2061 - AAAS, c. 1993)
The Physical Setting - Forces of Nature (4G)
By the end of the 12th grade, students should know that:
• There are two kinds of charges- positive and negative. Like charges
repel each other, opposite charges attract.
• Different kinds of materials respond differently to electric forces. In
conducting materials such as metals, electric charges flow easily.
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Current Electricity
Student Learning
Objectives
Upon viewing the video and completing the enclosed student
activities, students should be able to do the following:
•
Understand the various sources of electricity;
•
Discuss the concept of electric potential difference;
•
Define current and understand the role it plays in creating
electricity;
•
Understand the concept of resistance;
•
Define Ohm’s Law and understand the relationship between
current, voltage, and resistance;
•
Differentiate between direct and alternating current;
•
Identify the components of a circuit;
•
Differentiate between series and parallel circuits;
•
Understand the function of grounded plugs, fuses, and
breakers as safety features in electrical wiring; and
s•
Define electrical power and explain how it is calculated.
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Current Electricity
Assessment
Preliminary Test:
The Preliminary Test, provided in the Student Master section, is an
assessment tool designed to gain an understanding of student preexisting
knowledge. It can also be used as a benchmark upon which to assess
student progress on the objectives stated on the previous pages.
Video Review:
The Video Review, provided in the Student Masters section, can be used as
an assessment tool or as a student activity. There are two main parts. The
first part contains questions titled “You Decide” that can be answered during
the video. The second series of ten questions consists of video review
questions to be answered at the conclusion of the video.
Post-Test:
The Post-Test, provided in the Student Masters section, can be utilized as an
assessment tool following student completion of the video and student
activities. The results of the Post-Test can be compared against the results of
the Preliminary Test to assess student progress.
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Current Electricity
Introducing the
Video
Discuss and define the term electricity as a class. Next, divide
students into small groups. Ask each group to list the uses of
electricity that they see around them everyday. Ask one representative
from each group to write the lists on the board and discuss the answers
as a class. Next, ask each group to discuss some sources of electricity.
Remind them to consider terms such as current, circuit, and resistance.
Come together as a class and discuss the possible mechanisms behind
electricity production. Allow the lists to remain on the board during
the video. Upon the conclusion of the program, ask students to
discuss any new information they may have learned from the video.
Video Viewing
Suggestions
You may want to photocopy and distribute the Student Master “Video
Review”. You may choose to have your students complete this Master while
viewing the program or to do so upon its conclusion.
The program is approximately 20-minutes in length and includes a tenquestion video quiz. Answers are not provided to the Video Quiz on the
video, but are included in this teacher’s guide. You may want to grade
student quizzes as an assessment tool or to review the answers in class.
The video is content-rich with numerous vocabulary words. For this reason
you may want to periodically stop the video to review and discuss new
terminology and concepts.
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Current Electricity
Student Assessments
and Activities
Assessment Masters:
•
Preliminary Test
•
Video Review
•
Post-Test
Student Activity Masters:
•
Understanding Ohm’s Law
•
Electric Lemon
•
Electric Safety
•
Reading Electric Bills
•
Electricity in Your Home
•
Vocabulary of Current Electricity
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Current Electricity
Video Script
Current Electricity
1. This large dam...
2. ...and this generating plant were built to produce power so that people...
3. ...could use electricity to light their homes,...
4. ...cook their food,...
5. ...listen to music,...
6. ...watch television,...
7. ...and do work. Electricity is the result of flowing charges. How is electricity created and how does it
travel such great distances from its source all the way to our homes?
8. During the next few minutes, we are going to see how electricity is produced. We are also going to
explore how electricity is controlled and harnessed to be useful.
9. Graphic Transition - Sources of Electric Energy
10. Have you ever wondered where the electricity you use in your home originates?
11. You may know that it comes from a wire going into your home from the street or underground.
12. But where is the source of those wires?
13. Chances are they come from some type of electrical generator station or a large power plant.
14. Most power plants use an energy source such as coal, or oil,...
15. ...or moving water to create electricity.
16. Power plants may even utilize nuclear energy in the form of enriched uranium.
17. These energy sources directly or indirectly turn generators, which in turn produce electricity.
18. But electricity can also be produced by other sources, such as batteries.
19. You have probably used batteries ...
20. ...in toys, such as this car,...
21. ...or to start an engine, such as in this car.
22. Batteries rely on chemical reactions that occur inside the battery to create electricity.
23. Another source of electricity, although less common, is photocells or solar cells.
24. These cells take light energy and convert it to electricity.
25. All of these sources work on the same principle in that they create an electric potential difference.
26. Let’s take a look at electric potential difference.
27. Graphic Transition - Electric Potential Difference
28. Electric potential difference is the amount of work required to move a charge between two points.
29. This means that whenever there is a difference in charges between two points, charges will flow from
one point to another.
30. Potential difference is measured in units called volts.
31. Voltage is the amount of energy carried by charges. The voltage in the outlets in most homes is 120
volts.
32. But for some big appliances, like clothes dryers, the voltage needs to be 220 volts.
33. Graphic Transition - Electric Current
34. What a maze of wires! This is not really that unusual. In most homes, a similar network of wires...
35. ...runs to all parts of the house, supplying electricity for lights,...
36. ...computers,...
37. ...washing machines,...
38. ...and kitchen appliances. These wires form circuits. A circuit is a wire that forms a complete path in
which both ends are connected to an electrical source.
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Current Electricity
Script (cont.)
39. Electrical charges flow through a circuit. This is often referred to as current.
40. Current is the amount of charge that flows through a point per unit of time.
41. A current consists of flowing electrons. These flowing electrons commonly are conducted in a wire.
42. Current is expressed in units called amperes or amps. An amp is the amount of charge that flows past a
point per second.
43. This instrument is an ammeter. It shows about 4.5 amps of electricity are flowing through this wire.
44. The current in a metal wire is directly proportional to the potential difference applied at the source.
45. For example, the current flow in a wire connected to a 6-volt battery would be four times that of a wire
connected to a 1.5 volt battery.
46. Graphic Transition - Resistance
47. Notice how these rocks obstruct the flow of water in this stream, causing the water to bunch up. The
rocks resist the flow of water.
48. A similar phenomenon occurs as electrons flow through a metal wire. Resistance is the opposition to
the flow of electric charge.
49. Resistance is measured in units called ohms.
50. Some materials, such as this copper wire, have very low resistance to current electricity.
51. But other materials, such as rubber, have a very high resistance to electricity and allow little or no
electricity to flow through it.
52. A simple electric light bulb operates on the principle of resistance.
53. This bulb gives off light and heat. If you have ever touched a light bulb, you know that it is often very
hot after it has been turned on for a while. Electricity often produces heat when it runs into a resistor.
54. If you look closely inside a light bulb, you will notice a thin piece of metal called the filament.
55. The filament is made of a special type of metal that acts as a resistor, converting electricity to heat and
light.
56. The same phenomenon occurs in a toaster, with the wires inside acting as resistors that produce intense
heat.
57. Graphic Transition - Current, Voltage, and Resistance
58. It is possible to compute the current in a circuit if we know the voltage and resistance.
59. A scientist by the name of George Simon Ohm did many experiments with electricity. His work led to
an understanding of the relationship between current, voltage, and resistance.
60. This is stated in Ohm’s Law, which says that current is equal to voltage divided by resistance.
61. Let’s take an example. In this circuit the voltmeter reads about .5 volts...
62. ...and the ohmmeter reads 3.5 ohms.
63. When plugged into the formula, where .5 volts are divided by 3.5 ohms, we get a current of about .14
amps.
64. Graphic Transition - Current Direction
65. Amazingly, electrons can flow through a wire in a couple different ways. One way they can move is
continuously, in the same direction.
66. This is called direct current, or DC.
63. Electricity flowing from a battery is direct current.
67. But electrons can also reverse their direction regularly, moving back and forth. This is called
alternating current, or AC.
68. The electricity that we use in our homes and schools is alternating electricity.
69. The electricity found in most homes alternates or changes direction 120 times every second!
70. Graphic Transition - Circuits
71. You Decide ! This light bulb will not light. Study the picture for a moment. What is the problem?
72. That’s right, only one post on the battery is connected.
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Current Electricity
Script (cont.)
73. When we attach a wire to the other post, the bulb lights. This makes the circuit complete.
74. An electric circuit is a complete closed path on which an electric current flows.
75. An electric circuit has several parts. First, it must have a source of energy, such as a battery.
76. Second, it must have resistance or load, such as a light bulb. The load usually converts electricity to
light, mechanical energy, or heat energy.
77. Third, the circuit must have wires to carry the electric current.
78. Fourth, it has a switch. The switch closes and opens the circuit.
79. Electricity can only flow when the switch is on and electricity is allowed to flow. The circuit is now
closed. Electricity can only flow in a closed circuit.
80. Graphic Transition - Circuits
81. There are two main types of circuits - series circuits and parallel circuits. First, let’s take a look at series
circuits.
82. In a series circuit, there is only one way for the electrons to travel.
83. Series circuits were among the first type of electric circuits. The problem with series circuits is that if
there is a break in the circuit, the entire circuit shuts down.
84. Series circuits were among the first types of electrical circuits. The problem with series circuits is that
if there is a break in the circuit, the entire circuit shuts down.
85. This string of lights is wired in series - if one bulb is unscrewed, all of the lights in the string go out
because the circuit is open.
86. One way to solve the shortcomings of the series circuit is to use a parallel circuit.
87. In a parallel circuit, there are several paths electrons can take.
88. This is a parallel circuit with several light bulbs. If one of the bulbs were to burn out,...
89. ...notice how the others bulbs stay lit. The electrons find another path to follow and the circuit remains
closed.
90. These lights are wired in parallel. In parallel circuits, the parts of the circuit are on separate branches.
91. Graphic Transition - Circuits in Your Home
92. Believe it or not, this is what the wiring in your home looks like behind the walls.
93. This man is an electrician. His job is to safely set up electric circuits in buildings.
94. Most modern wiring looks like this, covered in a tough rubber casing.
95. Inside are three wires. The metal wires are made of copper - a very conductive metal.
96. The electric potential difference between them is 120 volts.
97. This wire is the ground wire. We will discuss the purpose of the ground wire in a minute.
98. These wires are connected to the back of an outlet, the part you usually do not see.
99. Therefore, when you plug a light into the outlet, each prong of the plug comes into contact with each
wire and makes a complete circuit.
100. Many appliances like this hand mixer have a third prong. This is the ground.
101. The purpose of the grounded plug is to protect against short circuits. A short circuit occurs when an
incorrect connection forces current to take a shorter path around a circuit.
102. If a short circuit occurs in the wire or appliance, it is grounded and the chance of being shocked is
greatly reduced.
103. Graphic Transition - Fuses and Breakers
104. Have you ever experienced a sudden loss of electricity when a lot of appliances, such as a coffee
maker, microwave, and light, were running at the same time?
105. This is a built-in safety feature in the electrical circuitry in your home.
106. The safety feature is in the metal box called a breaker box. These black switches are called breakers.
107. Breaker boxes are often located in the basement or in closets in the garage. Most homes have at least
one or two breaker boxes.
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Current Electricity
Script (cont.)
108. When a circuit becomes overloaded, it trips the breaker and the circuit is disconnected.
109. When this happens, it is necessary to turn off the appliances and then flip the breakers back on.
110. Older homes have fuses that work in a similar way. Fuses have a small thin piece of metal through
which runs electric current.
111. When the circuit overloads and the metal strip becomes too hot - it simply melts - and the circuit is
broken.
112. The problem with fuses, however, is that they must be replaced each time they blow with a new fuse
of correct amperage.
113. Graphic Transition - Electric Power
114. Power is the rate at which work is done, or the rate at which energy is utilized.
115. Power can be applied to things that use electricity.
116. For example, this toaster has the power of about 700 watts.
117. Electric power is the rate at which electricity provides energy or does work.
118. Electric power can be computed by multiplying the voltage by the current.
119. Let’s put this formula to use by computing the electric power of the common light bulb.
120. We know that the voltage in this house is 120 volts.
121. The light bulb represents a resistance, or utilizes a current of about .33 amps.
122. When multiplied, we can see that the electric power consumed by the bulb is 40 watts.
123. If we look at the top of the bulb, we can see that is says 40 watts.
124. You Decide! Which bulb has a higher voltage?
125. That’s right! The bulb on the left has a higher voltage. It is a 75 watt bulb and is brighter that the 40
watt bulb on the right.
126. You have probably noticed meters like this on the outside or the inside of buildings. These devices
are called electric meters and measure the current of electric energy that flows into the building.
127. Notice the moving dial on the meter. It is reading the amount of electricity flowing.
128. Electric energy is the amount of power per unit time.
129. Electric energy is commonly measured in kilowatt-hours, which is 1000 watts of power used for one
hour.
130. Electric bills are based on the amount of kilowatt hours utilized over a period of time.
131. Graphic Transition - Summing Up
132. In the past few minutes we have explored current electricity.
133. We began by investigating the sources of electrical energy, such as generators....
134. ...and batteries.
135. We studied electric potential difference, as well as voltage.
136. We took a look at electrical current and current direction.
137. And we explored the concept of resistance, as well as Ohm’s Law of Resistance.
138. We also learned about different types of circuits and how they function.
139. Finally, we explored electric power and how it can be computed using a mathematical formula.
140. So the next time you use a light, work on a computer, or listen to music, take a minute to think about
how electricity affects our lives. You might just think about electrical energy a little differently.
Video Quiz
Fill in the correct word when the question appears on the screen. Good luck and let’s get started.
1. A ___________ is a device used to produce electricity.
2. Electric ________ difference is the amount of work required to move a charge between two points.
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Current Electricity
Script (cont.)
3. A _______ is a wire that forms a complete path in which both ends are connected to an
electrical source.
4. The amount of charge that flows through a point per unit time is called ________.
5. ________ is the opposition to the flow of electric charge.
6. Resistance is measured in units called _____.
7. Electricity can only flow in a ______ circuit.
8. The third prong on an electric plug acts as the _______.
9. Breaker boxes and ______ are two safety features built into the electrical wiring of your home.
10. Electric _______ is the rate at which electricity provides energy or does work.
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Current Electricity
Answers to Student
Assessments
Preliminary Test
1. generators
2. direct
3. voltage
4. circuits
5. current
6. ampere
7. resistance
8. parallel
9. breaker
10. power
11. False
12. True
13. False
14. True
15. True
16. True
17. False
18. True
19. True
20. False
Video Quiz:
1. generator
2. potential
3. circuit
4. current
5. resistance
6. Ohms
7. closed
8. ground
9. fuses
10. power
Post Test
1. False
2. False
3. True
4. False
5. True
6. True
7. True
8. True
9. False
10. True
11. current
12. parallel
13. voltage
14. circuits
15. generators
16. breaker
17. resistance
18. power
19. ampere
20. direct
Video Review
You Decide:
A. Only one post on the battery is
connected.
B. The bulb on the left as a higher voltage.
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Current Electricity
Answers to Student
Activities
Understanding Ohm’s Law
1. 12 ohms
2. 14.7 amps
3. 225 volts
4. .4 amps
5. 337.5 volts
6. 35 ohms
4. Temperature probably increased
and more cooling appliances were
used.
5. 1999
6. It was hotter in September of 1999 more cooling appliances were
probably used.
7. Electric heat, stoves and space
heaters could be used to heat the
home. Fans and air-conditioners
could be used to cool the home.
8. Answers will vary.
Electric Lemon
Conclusions: Yes, an electric current is
produced. Softening the lemon breaks
its cellular structure apart and allows
citric acid to dissolve into a water
solution. When citric acid is in a water
solution, the hydrogen ions act as
electrolytes with the ability to conduct a
current. Answers will vary.
Electricity in Your Home
Conclusions: Answers will vary. You
can save on electricity costs by turning
off all electrical appliances when not in
use.
Electric Safety
1. False
2. True
3. False
4. False
5. False
Vocabulary Lesson
1. Ohm’s law, b
2. direct current, d
3. amperes, e
4. electrical power, j
5. alternating current, a
6. series circuit, f
7. current, h
8. parallel circuit, g
9. resistance, c
10. electric circuit, i
Reading Electric Bills
1. December
2. September
3. The temperature probably
decreased and more heating
appliances were probably used.
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Assessment
and Student
Activity
Masters
18
Current Electricity
Name___________________
Preliminary Test
Directions: Fill in the blank with the correct word. A list of possible
answers is provided at the bottom of the page.
1. _____________ produce electricity from a variety of fuels including coal, gas,
and oil.
2. When electrons move through a wire continuously in one direction, they form a
________ current.
3. __________ is the amount of energy carried by charges.
4. The mazes of wires found in most homes form ___________.
5. Electrical charge flowing through a circuit is referred to as ___________.
6. An _________ is the amount of charge that flows past a point per second.
7. A simple electric light bulb operates on the principle of ____________.
8. In __________ circuits, electrons can follow a variety of paths.
9. __________ boxes and fuses are two safety features built into the electrical
circuitry in your home.
10. Electric ________ can be computed by multiplying the voltage by the
current.
power
ampere
voltage
direct
circuits
potential difference
current
generators
resistance
parallel
breaker
closed
19

Current Electricity
Name___________________
Preliminary
Test
Directions: Decide whether the answer is True (T) or False (F).
11. Potential difference is measured in watts.
T
F
12. Solar cells trap light energy from the sun
and convert it to electricity.
T
F
13. Current is expressed in units called ohms.
T
F
14. Current can either be direct or alternating.
T
F
15. The greater the opposition to the flow of
current, the higher the resistance.
T
F
16. The thin piece of metal inside a light bulb
is called a filament.
T
F
17. Electricity can only flow in an open circuit.
T
F
18. In a series circuit, there is only one path
electrons can follow.
T
F
19. Electric energy is the amount of power per
unit time.
T
F
20. Ohm’s Law states that voltage is equal to
current divided by resistance.
T
F
20

Current Electricity
Name___________________
Video Review
Directions: During the course of the program answer the “You Decide”
questions as they are presented in the video. Answer the Video Quiz
questions at the end of the video.
You Decide:
A. This light bulb will not light. What is the
problem?
Answer: _______________
B. Which bulb has a higher voltage?
Answer: _______________
Video Quiz:
1. A ______________ is a device used to produce electricity.
2. Electric ___________ difference is the amount of work required to move a charge
between two points.
3. A __________ is a wire that forms a complete path in which both ends are connected
to an electrical source.
4. The amount of charge that flows through a point per unit time is called ___________.
5. ______________ is the opposition to the flow of electric charge.
6. Resistance is measured in units called ____________.
7. Electricity can only flow in a ___________ circuit.
8. The third prong on an electric plug acts as the ___________.
9. Breaker boxes and __________ are two safety features built into the electrical wiring
of your home.
10. Electric __________ is the rate at which electricity provides energy or does work.
21

Current Electricity
Name___________________
Post Test
Directions: Decide whether the answer is True (T) or False (F).
1. Current is expressed in units called ohms.
T
F
2. Ohm’s Law states that voltage is equal to
current divided by resistance.
T
F
3. Electric energy is the amount of power per
unit time.
T
F
4. Electricity can only flow in an open circuit.
T
F
5. The thin piece of metal inside a light bulb
is called a filament.
T
F
6. The greater the opposition to the flow of
current, the higher the resistance.
T
F
7. Current can either be direct or alternating.
T
F
8. In a series circuit, there is only one path
electrons can follow.
T
F
9. Potential difference is measured in watts.
T
F
10. Solar cells trap light energy from the sun
and convert it to electricity.
T
F
22

Current Electricity
Name___________________
Post Test
Directions: Fill in the blank with the correct word. A list of possible
answers is provided at the bottom of the page.
11. Electrical charge flowing through a circuit is referred to as ________.
12. In __________ circuits, electrons can follow a variety of paths.
13. __________ is the amount of energy carried by charges.
14. The mazes of wires found in most homes form ___________.
15. _____________ produce electricity from a variety of fuels including coal,
gas, and oil.
16. __________ boxes and fuses are two safety features built into the electrical
circuitry in your home.
17. A simple electric light bulb operates on the principle of ____________.
18. Electric ________ can be computed by multiplying the voltage by the
current.
19. An _________ is the amount of charge that flows past a point per second.
20. When electrons move through a wire continuously in one direction, they form
a ________ current.
power
ampere
voltage
direct
circuits
potential difference
current
generators
resistance
parallel
breaker
closed
23

Current Electricity
Name___________________
Understanding Ohm’s
Law
Background:
Chances are you have turned on a light bulb today and watched it glow with
light. Have you ever wondered how a light bulb gives off light? Light bulbs
operate on the principle of resistance. Resistance is a material’s opposition
to the flow of electrons. A light bulb contains a thin piece of metal called
the filament that acts as a conductor. As a current flows through the
filament, it encounters resistance and the electromagnetic energy is
converted to light and heat energy. The light energy results in the light we
see and the heat energy is what causes the light bulb to become very hot.
All conductors have a certain amount of resistance.
Scientist George Simon Ohm did a series of experiments to determine the
relationship among current, resistance, and voltage. Ohm’s Law states that
the current in a wire equals the voltage divided by the resistance.
Current (amps)
=
Voltage (V)
Resistance (ohms)
Directions: Using the information provided above, complete the following
chart. You may use the back of this page for your calculations.
Amps
Volts
10
120
250
15
17
15
12
7.5
5
Ohms
30
45
175
24
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Current Electricity
Name___________________
Electric Lemon
Objective:
In this lab you will create electricity using a lemon, zinc pieces, and copper wire.
Background:
The electricity we use in our homes is produced by generators in power plants. But did
you know that electricity can be produced by something as simple as a lemon and some
pocket change? You have all probably tasted the bitterness of a lemon. This is caused by
citric acid. When dissolved in water, acids will split apart to form hydrogen ions. An
electrolyte is a substance that can conduct an electric current when in a water solution.
When the lemon in this experiment is softened, the citric acid will break down into
hydrogen ions, thus becoming a conductor of electric current.
Materials:
Voltmeter
Lemon
Two pieces of zinc (or two pennies)
Copper wire
Scissors
Procedure:
1. Wrap the copper wire around each piece of zinc. Place the zinc pieces about 1 inch
apart.
2. Connect each end of the wire to the voltmeter. One end should be connected to the
positive terminal and the other to the negative terminal. Make sure the voltmeter is
on.
3. Soften a lemon by rolling it back and forth on a surface while exerting a bit of
pressure with the palm of your hand. Using a pair of scissors, slice two slits in the
lemon, approximately the same size as the zinc pieces. Caution: Be careful not to cut
yourself!
4. Slip each zinc piece into its own slit.
5. Record the voltage measured by the voltmeter.
6. Switch the wire connections to the voltmeter and record the new voltage.
Conclusions:
Is an electric current produced? What is accomplished by softening the lemon? How
does the lemon conduct a current? Is there any difference in voltage when the wire
connections are switched?
25
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Current Electricity
Name___________________
Electric Safety
Background:
Electricity is an important source of energy in our everyday lives. It is
also a very dangerous resource and must be respected by following a few
basic ground rules. First, electricity should never be used in the direct
vicinity of water. The presence of water could result in electrocution as a
result of the formation of an electrical circuit. You should never approach
fallen power lines since these wires often conduct high voltages. Wires
should never be allowed to remain frayed or worn. Frayed wires could
result in short circuits and fires if found near or under a carpet. Always
keep fingers or other objects away from electric sockets. Electricity could
be conducted through whatever object is in the socket or even directly into
your finger and through your body. Finally, the number of appliances
connected to a socket should correspond to the socket’s potential. Fuses
will fail if this potential is exceeded and electricity can be temporarily lost.
Directions: Decide whether the following statements are True (T) or False
(F) based on the information provided above.
1. It is dangerous to blow dry your hair if it is raining
outside.
T
F
2. It is unsafe to connect all the appliances in your home
to one socket.
T
F
3. It is perfectly safe to stick a spoon in an electrical
socket.
T
F
4. It is safe to hide all the wires in a room by running
them under a rug.
T
F
5. It is safe to pick up an object that is lying next to a
fallen power line.
T
F
26
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Current Electricity
Name___________________
Reading Electric Bills
Directions: Use the information provided below to answer the questions on the
following page.
Background:
Each month you receive an electric bill that charges you for the amount of
electricity your home has used in the previous month. But do you know what all
the information on that bill means? First, there is a billing portion where the
number of kilowatt-hours used is multiplied by a base rate, usually about 10
cents per kilowatt-hour, give or take a few cents. This gives you your monthly
electricity costs. Also included in an electric bill is a section that allows you to
compare your electricity use throughout the year. This section will include a
monthly comparison for the previous year as well as a comparison between the
present month and that same month one year earlier. This information can help
customers understand increases in bills as well as trends in their use of
electricity. The data below is for a house located in northern New England.
Billing Period
KWH used
Billing Days
Avg Temperature
September 1999
626
33
75
September 1998
452
29
66
12 Month Comparison
KWH
per month
Month
27
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Current Electricity
Name___________________
Reading Electric Bills
1. During which month were the most kilowatt-hours used?
2. During which month were the least kilowatt-hours used?
3. List some possible reasons why electricity use increased from November
to December.
4. List some possible reasons why electricity use increased during the
months of June and July.
5. Was more electricity used in September of 1999 or September of 1998?
6. List some possible reasons why more electricity was used in your answer
to number 5.
7. What are some common appliances used to heat your homes in the winter
and cool your homes in the summer?
8. Brainstorm some possible ways to cut down on heating and
air-conditioning use in your homes.
28
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Current Electricity
Name___________________
Electricity in Your
Home
Objective:
In this activity you will learn how to approximate the amount of electricity used by
certain appliances in your home.
Background:
Most of us have numerous electrical appliances in our homes, such as a
refrigerator, a television, a hair-dryer, or a light bulb. Using these appliances is not
free. An electric bill comes each month, charging you for the amount of electricity
you have used. Every appliance has a power rating measured in units called watts.
This power rating can be used to calculate the amount of electricity used by that
appliance. The equation used to calculate the amount of energy used by an
appliance in one day is as follows:
Energy (kWh) = power (kW) x time (h)
The current electricity rate is approximately 10 cents per unit, or kilowatt-hour.
You can calculate the cost of using an appliance by multiplying the kilowatt-hours
used by the cost per unit.
Procedure:
1. Pick five electrical appliances that you use in your household daily. Record
the power rating of each of these appliances. This number may be found on
the back of the appliance.
2. Estimate the number of hours per day that you use each of these appliances.
3. Create a data chart including sections for the name of each appliance, the
hours of use, power ratings, the energy used, and the daily cost of each
appliance.
4. Using the equation above, calculate the amount of energy in kilowatt-hours
used by each appliance and the cost of using that appliance for one day.
Complete you data chart by placing these calculations in the appropriate
column.
Conclusions:
Which appliance uses the most energy? Is this the result that you expected? What
are some possible ways to save on electricity costs in your home?
29
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Current Electricity
Name___________________
Vocabulary of Current
Electricity
Directions: Unscramble the following vocabulary words and match each
word with its correct definition.
___ 1. mohs’ wla
a. current in which electrons regularly
reverse their direction of flow
___ 2. tcride rrtucne
b. states that current is equal to voltage
divided by resistance
___ 3. apsemre
c. opposition to the flow of electric
charge
___ 4. leclaertic oprwe
___ 5. lngtaeraitn ntrucre
d. current in which electrons flow in
one continuous direction
e. amount of charge that flows past a
point per second
___ 6. sierse turicci
f. circuit in which electrons have only
one path to follow
___ 7. trenruc
g. circuit in which electrons have more
than one path to follow
___ 8. lllrpaae trcciui
h. the flow of electric charge
___ 9. ssceneirta
i. a complete closed path on which an
electric current flows
___ 10. cletecri uiccrti
j. the rate at which electric power
provides energy or does work
30
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