1. An energy efficient LED light bulb uses 5 W of power for an equivalent light

Question

1. An energy efficient LED light bulb uses 5 W of power for an equivalent light output of a 60 W incandescent light bulb. How much money do you save each month by using the energy efficient light bulb instead of the incandescent light bulb for 6 hours a day? Assume that 1 kWhr costs 12 cents and there are 30 days in one month.

2.   A 12-V car battery may supply 60 A for 2.5 s in order for the starter motor to start the engine. The electrical energy used during that time is

Explanation / Answer

Energy saved is

E = (60 W - 55 W ) * 6 hrs /day * 30days /1000 = 9.9kwh

Cost saved is 9.9kwh* $0.12 = $1.19

b) E = P * t = V I t = (12)(60)(2.5) = 1800 J

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