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Chapter Review
Moving electric charges transfer energy.
CONTENT REVIEW
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KEY CONCEPTS SUMMARY
1
Materials can become electrically charged.
electric charge p. 634
electric field p. 634
static charge p. 635
induction p. 637
Electric charge is a property of matter.
Electrons have a
negative charge.
Protons have a
positive charge.
Unlike charges
attract.
VOCABULARY
Like charges repel.
Static charges are caused by the movement of electrons, resulting
in an imbalance of positive and negative charges.
2
Charges can move from one place to another.
Charge movement is affected by
• electric potential, measured
in volts
• resistance, measured in ohms
A conductor has low resistance.
An insulator has high resistance.
A ground is the path of least
resistance.
3
Electric current is a flow of charge.
Electric current is measured in amperes, or amps.
Ohm’s law states that current equals voltage
divided by resistance.
Electrochemical cells produce electric current
through chemical reactions.
660 Unit 5: Electricity and Magnetism
VOCABULARY
electric potential p. 643
volt p. 643
conductor p. 646
insulator p. 646
resistance p. 647
ohm p. 647
grounding p. 649
VOCABULARY
electric current p. 652
ampere p. 653
Ohm’s law p. 653
electric cell p. 655
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Reviewing Vocabulary
Copy the chart below, and write each term’s
definition. Use the meanings of the underlined
roots to help you.
Word
EXAMPLE
current
Root
to run
1. static
charge
standing
2. induction
into + to lead
3. electric
cell
chamber
Definition
continuous
flow of charge
4. conductor with + to lead
5. insulator
island
6. resistance to stop
7. electric
potential
power
8. grounding
surface of
Earth
13. A static charge is different from electric current
in that a static charge
a. never moves
b. can either move or not move
c. moves only when resistance is low enough
d. moves only when voltage is high enough
14. Charging by induction means charging
a. with battery power
b. by direct contact
c. at a distance
d. using solar power
15. Electric potential describes
a. the electric potential energy per unit charge
b. the electric kinetic energy per unit charge
c. whether an electric charge is positive or
negative
d. how an electric charge is affected by gravity
16. A superconductor is a material that, when
very cold, has no
a. amperage
b. resistance
c. electric charge
d. electric potential
Write a vocabulary term to match each clue.
9. In honor of scientist Alessandro Volta
(1745–1827)
10. In honor of the scientist who discovered the
relationship among voltage, resistance, and
current
11. The amount of charge that flows past a given
point in a unit of time.
17. Ohm’s law says that when resistance goes
up, current
a. increases
c. stays the same
b. decreases
d. matches voltage
18. Electrochemical cells include
a. all materials that build up a charge
b. primary cells and storage cells
c. batteries and solar cells
d. storage cells and lightning rods
Reviewing Key Concepts
Multiple Choice Choose the letter of the
best answer.
Short Answer Write a short answer to
each question.
12. An electric charge is a
a. kind of liquid
b. reversible chemical reaction
c. type of matter
d. force acting at a distance
19. What determines whether a charge you
get when walking across a rug is positive
or negative?
20. What is the difference between resistance
and insulation?
21. What is one disadvantage of solar cells?
Chapter 19: Electricity 661
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Thinking Critically
Using Math in Science
Use the diagram of an electrochemical cell
below to answer the next three questions.
Use the formula for Ohm’s law to answer the
next four questions.
V
R
I negative
terminal
positive
terminal
electrolyte
electrode
electrode
22. ANALYZE In which direction do electrons flow
between the two terminals?
23. PREDICT What changes will occur in the cell as
it discharges?
28. An electrical pathway has a voltage of 240
volts and a current of 10 amperes. What is
the resistance?
29. A 240-volt air conditioner has a resistance of
8 ohms. What is the current?
30. An electrical pathway has a current of 1.2
amperes and resistance of 40 ohms. What is
the voltage?
31. An electrical pathway has a voltage of 400
volts and resistance of 2000 ohms. What is
the current?
24. ANALYZE What determines whether the cell is
rechargeable or not?
Use the graph below to answer the next three
questions.
high
resistance
low
resistance
32. INFER Look back at the photograph on pages
630 and 631. Based on what you have learned
in this chapter, describe what you think is
happening to keep the dragon lit.
33. COMPARE AND CONTRAST Draw two simple
diagrams to compare and contrast static
charges and electric current. Add labels and
captions to make your comparison clear. Then
write a paragraph summarizing the comparison.
co
pp
ge
er
rm
PV
an
iu
m
C
pl
as
t
ics
25. INFER Which material could you probably use
as an insulator?
26. INFER Which material could be used in a
lightning rod?
27. APPLY Materials that conduct electrons under
some—but not all—conditions are known as
semiconductors. Which material is probably a
semiconductor?
662 Unit 5: Electricity and Magnetism
If you are doing a unit project, make a folder for
your project. Include in your folder a list of the
resources you will need, the date on which the
project is due, and a schedule to keep track of
your progress. Begin gathering data.
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Standardized Test Practice
For practice on your
state test, go to . . .
TEST PRACTICE
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Interpreting Diagrams
Use the illustration below to answer the following questions. Assume that
the balloons start off with no net charge.
–
+
+
–
+
–
+ –
1. What will happen if a negatively charged rod
is brought near one of the balloons without
touching it?
a. The balloons will move toward each other.
b. The balloons will move away from each other.
c. Electrons on the balloons will move toward
the rod.
d. Electrons on the balloons will move away from
the rod.
2. What will happen if a positively charged rod
is brought near one of the balloons without
touching it?
a. The balloons will move toward each other.
b. The balloons will move away from each other.
c. Electrons on the balloons will move toward
the rod.
d. Electrons on the balloons will move away from
the rod.
Extended Response
Answer the two questions below in detail. Include
some of the terms from the word box. Underline
each term that you use in your answers.
7. Describe the events leading up to and including a
bolt of lightning striking Earth from a storm cloud.
3. In the previous question, the effect of the rod on
the balloons is an example of
a. charging by contact
c. induction
b. charge polarization
d. conduction
4. What will happen if a negatively charged rod is
brought near one of the balloons and the balloons
are then separated?
a. The balloon farthest from the rod will become
positively charged.
b. The balloon farthest from the rod will become
negatively charged.
c. Both balloons will become positively charged.
d. Both balloons will have no net charge.
5. If you rub one balloon in your hair to charge it
and then move it close to the other balloon, the
balloons will
a. not move
b. move away from each other
c. move toward the ground
d. move toward each other
6. What will happen if a negatively charged rod is
brought near one of the balloons, then taken
away, and the balloons are then separated?
a. The balloon farthest from the rod will become
positively charged.
b. The balloon farthest from the rod will become
negatively charged.
c. Both balloons will become positively charged.
d. Both balloons will have no net charge.
charge separation recharging resistance
source of current static charge induce
8. Explain the advantages and disadvantages of
storage cells over other types of electric cells.
Chapter 19: Electricity 663