Question

A 4watt night light is left on for 8 hours each night. how much work does it do per night

Answer 1

Power = (work) / (time)

Work = (power) x (time)

          = (4 watts) x (8 hours)

1 "watt" = 1 joule/sec .

Work = (4 joule/sec) x (8 hours) x (3,600 sec/hr)

         = (4 x 8 x 3,600) joules  =  1,024 joules .

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Another way:

4 watts = 0.004 kilowatt

Work = energy = (power) x (time)

                        = (0.004 kw) x (8 hrs)  =  0.032 kilowatt-hour .