Question

A 15W fluorescent light bulb uses operates for 30 minutes and produces 20kJ of light energy, what is the percent efficiency of the light bulb? Show work.

Answer 1

Given that ;

Energy (work ) Produced by bulb =20 KJ = 20000 J

Input power = 15 KW

Output power given by the bulb  = Rate of doing work

                                                   = Work ÷ time

                                                   = 20000 ÷ 1800   (since 1 min = 60 seconds)

                                                   = 11.11 W

Noe, efficiency is the ratio of output power to input power

                                                   η = output power ÷ input power

                                                      = 11.11 ÷ 15

                                                      = 0.74

                                                      = 74%

Efficiency of light bulb is 74%

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