Question

A certain 100W light bulb has an efficiency of 95%. How much thermal energy will this light bulb add to the inside of a room in 2.5h if the bulb is on for the whole time?

Answer 1

Since the bulb consumes 100 watts of power and its efficiency is 95%,
it generates 95 watts of light energy and 5 watts of heat energy whenever
it's turned on.

5 watts means  5 joules of energy per second.

(2.5 hours) x (3,600 seconds/hour) =  9,000 seconds

(9,000 seconds) x (5 joules/second)  =  45,000 joules of heat in 2.5 hours