Name
Date
Electric Circuits
Power and Work
Instructions: Do every problem using LEPA on a separate sheet of paper.
1. A 3.6-volt battery is used to operate a cell phone for an hour. If the cell phone draws a
current of 0.018 Amperes during that time, what is the energy lost by the battery? 233.28 J
2. What is the resistance of a 70-watt light bulb operated at 90 volts? 115.71 Ω
3. How much energy is dissipated in 10 seconds in a 4.0-ohm resistor with a current of 3
amperes? 360 J
4. An electrical appliance draws 7.0 amperes of current when connected to a 120-volt outlet.
What is the total amount of power dissipated by this appliance? 840 W
5. A 3.5-volt personal stereo uses 2000 joules of electrical energy in one hour. What is the
electrical resistance of the personal stereo? 22.05 Ω
6. To increase the brightness of a desk lamp, a student replaces a 50-watt incandescent light
bulb with a 100-watt incandescent light bulb. Compared to the 50-watt light bulb, the
100-watt light bulb has
a. less resistance and draws more current
b. less resistance and draws less current
c. more resistance and draws more current
d. more resistance and draws less current
7. A device operating at a potential difference of 1.5 volts draws a current of 0.2 ampere.
How much energy is used by the device in 60 seconds? 18 J
8. A light bulb operating at 120 volts draws a current of 0.35 ampere for 240 seconds. What
is the power rating of the light bulb? 42 W
9. An electric heater operating at 120 volts draws 4 amperes of current through its 30 ohms
of resistance. What is the total amount of heat energy produced by the heater in half an
hour? 8.64×105 J
10. An air conditioner has a power rating of 2400 watts. If the air conditioner draws 20
amperes of current, what is the resistance of the air conditioner? 6 Ω