Answer to Question #158326 in Physics for ha na

Question

Calculate the efficiency of the following devices

A lamp which converts 17 W out of every 20 W into thermal energy. The lamp is being used for the sole purpose of lighting the room.

Answer 1

Since the purpose of the lamp is to light the room, not heat it up, only 3 W are used for lighting. Thus, the efficiency is

$$\eta=\frac{3}{20}\cdot100\%=15\%.$$