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Power Worksheet

1. What does the power rating on a light bulb describe?

Power is the rate of consumption of energy. So the power rating tells us how many Joules per second the light bulb consumes.

2. If the resistance of a light bulb is increased, how will the electrical energy used by the light bulb over the same period of time change?

R is in the denominator, so as R rises, P falls.

3. How much does it cost to watch a 300 W television for 24 hours? Assume that electrical energy costs $0.30 / kWh.

4. An electric heater is operated by applying a 120 V across a wire with a resistance of 16Ω. Find the current and the power rating of the heater.

5. For each of the following devices, calculate the unknown quantities. (Show calculations on the back of this sheet, then fill in the blanks.)

Device	Power	Resistance	Current	Voltage
Computer	132 W	92Ω	1.2 A	110 V
Portable stereo	12 W	0.75 Ω	4 A	3.0 V
Coffee maker	600 W	24 Ω	5.0 A	120 V
Calculator	0.16 W	230 Ω	26 mA	6.0 V
Incandescent light bulb	100 W	140 Ω	0.83 A	120 V
Compact Florescent light bulb	13 W	1100 Ω	0.108 A	120 V
Microwave oven	960 W	15 Ω	8 A	120 V

Computer

Stereo

Coffee maker

Calculator

Incandescent bulb

CFL

Microwave Oven