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Group A—Continued Group B—Continued
8. A lightbulb with a resistance of 10.0 Ω allows a 1.20 A current to 8. A 10.0 Ω lightbulb is connected to a 12.0 V battery. (a) What
flow when connected to a battery. (a) What is the voltage of the current flows through the bulb? (b) What is the power of
battery? (b) What is the power of the lightbulb? the bulb?
9. A small radio operates on 3.00 V and has a resistance of 15.0 Ω. 9. A lightbulb designed to operate in a 120.0 V circuit has a
At what rate does the radio use electric energy? resistance of 192 Ω. At what rate does the bulb use electric
energy?
10. A 1,200 W hair dryer is operated on a 120 V circuit for 15 min. 10. What is the monthly energy cost of leaving a 60 W bulb on
If electricity costs $0.10/kWh, what was the cost of using the continuously if electricity costs $0.10 per kWh?
blow dryer?
11. An automobile starter rated at 2.00 hp draws how many amps 11. An electric motor draws a current of 11.5 A in a 240 V circuit.
from a 12.0 V battery? What is the power of this motor in W?
12. An average-sized home refrigeration unit has a 1/3 hp fan motor 12. A swimming pool requiring a 2.0 hp motor to filter and circulate
for blowing air over the inside cooling coils, a 1/3 hp fan motor the water runs for 18 hours a day. What is the monthly electrical
for blowing air over the outside condenser coils, and a 3.70 hp cost for running this pool pump if electricity costs $0.10 per
compressor motor. (a) All three motors use electric energy at kWh?
what rate? (b) If electricity costs $0.10/kWh, what is the cost of
running the unit per hour? (c) What is the cost of running the
unit 12 hours a day for a 30-day month?
13. A 15 ohm toaster is turned on in a circuit that already has a 13. Is it possible for two people to simultaneously operate 1,300 W
0.20 hp motor, three 100 W lightbulbs, and a 600 W electric iron hair dryers on the same 120 V circuit without tripping a 15 A
that are on. Will this trip a 15 A circuit breaker? Explain. circuit breaker? Explain.
14. A power plant generator produces a 1,200 V, 40 A alternating 14. A step-up transformer has a primary coil with 100 loops and a
current that is fed to a step-up transformer before transmission secondary coil with 1,500 loops. If the primary coil is supplied
over the high lines. The transformer has a ratio of 200 to 1 wire with a household current of 120 V and 15 A, (a) what voltage is
loops. (a) What is the voltage of the transmitted power? (b) What produced in the secondary circuit? (b) What current flows in the
is the current? secondary circuit?
15. A step-down transformer has an output of 12 V and 0.5 A when 15. The step-down transformer in a local neighborhood reduces the
connected to a 120 V line. Assume no losses. (a) What is the voltage from a 7,200 V line to 120 V. (a) If there are 125 loops on
ratio of primary to secondary loops? (b) What current does the the secondary, how many are on the primary coil? (b) What
transformer draw from the line? (c) What is the power output of current does the transformer draw from the line if the current in
the transformer? the secondary is 36 A? (c) What are the power input and output?
16. A step-up transformer on a 120 V line has 50 loops on the 16. A step-down transformer connected to a 120 V electric generator
primary and 150 loops on the secondary, and draws a 5.0 A has 30 loops on the primary for each loop in the secondary.
current. Assume no losses. (a) What is the voltage from the (a) What is the voltage of the secondary? (b) If the transformer
secondary? (b) What is the current from the secondary? has a 90.0 A current in the primary, what is the current in the
(c) What is the power output? secondary? (c) What are the power input and output?
17. Two 8.0 Ω lightbulbs are connected in a 12 V series circuit. What 17. What is the power of an 8.0 ohm bulb when three such bulbs are
is the power of both glowing bulbs? connected in a 12 volt series circuit?

176 CHAPTER 6 Electricity 6-38