Question

A lightbulb has an efficiency of 13.1%. How much light energy (not heat energy) is generated by the bulb every second if the bulb has a power of 8W?

A. 6.95J
B. 2.21J
C. 1.05J
D. 3.49J

Answer 1

It's answer C) 1.05J.
The light bulb produces \[8W=8Js ^{-1}\] at 13.1% efficiency, hence only 13.1% of the total power is light. \[8\times0.131=1.048Js ^{-1}\]