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2. What are the significant similarities and differences between ac
QUESTIONS FOR THOUGHT
and dc? What determines which is better for a particular
application?
1. Explain why a balloon that has been rubbed sticks to a wall 3. Transformers usually have signs warning, “Danger—High
for a while. Voltage.” Analyze if this is a contradiction since it is exposure to
2. Explain what is happening when you walk across a carpet and amps, not volts, that harms people.
receive a shock when you touch a metal object. 4. Will a fuel cell be the automobile engine of the future? Identify
3. Why does a positively or negatively charged object have the facts, beliefs, and theories that support or refute your
multiples of the fundamental charge? answer.
4. Explain how you know that it is an electric field, not electrons, 5. Analyze the apparent contradiction in the statement that “solar
that moves rapidly through a circuit. energy is free” with the fact that solar cells are too expensive to
use as a significant energy source.
5. Is a kWh a unit of power or a unit of work? Explain.
6. What are the basic similarities and differences between an
6. What is the difference between ac and dc?
electric field and a magnetic field?
7. What is a magnetic pole? How are magnetic poles named?
7. What are the advantages and disadvantages of using parallel
8. How is an unmagnetized piece of iron different from the same circuits for household circuits?
piece of iron when it is magnetized?
9. Explain why the electric utility company increases the voltage of
electricity for long-distance transmission.
10. Describe how an electric generator is able to generate an electric
current. INVITATION TO INQUIRY
11. Why does the north pole of a magnet point to the geographic
North Pole if like poles repel? Earth Power?
12. Explain what causes an electron to move toward one end of a Investigate if you can use Earth’s magnetic field to induce an electric
wire when the wire is moved across a magnetic field. current in a conductor. Connect the ends of a 10 m (about 33 ft) wire
to a galvanometer. Have a partner hold the ends of the wire on the
galvanometer while you hold the end of the wire loop and swing the
FOR FURTHER ANALYSIS double wire like a skip rope.
If you accept this invitation, try swinging the wire in different
1. Explain how the model of electricity as electrons moving along a directions. Can you figure out a way to measure how much electricity
wire is an oversimplification that misrepresents the complex you can generate?
nature of an electric current.

PARALLEL EXERCISES

The exercises in groups A and B cover the same concepts. Solutions to group A exercises are located in appendix E.
Group A Group B
1. A rubber balloon has become negatively charged from being 1. An inflated rubber balloon is rubbed with a wool cloth until an
rubbed with a wool cloth, and the charge is measured as excess of a billion electrons is on the balloon. What is the
–14
1.00 × 10 C. According to this charge, the balloon magnitude of the charge on the balloon?
contains an excess of how many electrons?
–14
2. One rubber balloon with a negative charge of 3.00 × 10 C is 2. What is the force between two balloons with a negative charge of
–10
suspended by a string and hangs 2.00 cm from a second rubber 1.6 × 10 C if the balloons are 5.0 cm apart?
–12
balloon with a negative charge of 2.00 × 10 C. (a) What is the
direction of the force between the balloons? (b) What is the
magnitude of the force?
3. A dry cell does 7.50 J of work through chemical energy to 3. How much energy is available from a 12 V storage battery that
transfer 5.00 C between the terminals of the cell. What is the can transfer a total charge equivalent to 100,000 C?
electric potential between the two terminals?
4. An electric current through a wire is 6.00 C every 2.00 s. What is 4. A wire carries a current of 2.0 A. At what rate is the charge
the magnitude of this current? fl owing?
5. A 1.00 A electric current corresponds to the charge of how many 5. What is the magnitude of the least possible current that could
electrons flowing through a wire per second? theoretically exist?
6. There is a current of 4.00 A through a toaster connected to a 6. There is a current of 0.83 A through a lightbulb in a 120 V
120.0 V circuit. What is the resistance of the toaster? circuit. What is the resistance of this lightbulb?
7. What is the current in a 60.0 Ω resistor when the potential 7. What is the voltage across a 60.0 Ω resistor with a current of
difference across it is 120.0 V? 3 1/3 amp?

6-37 CHAPTER 6 Electricity 175