Question

A light bulb has a power rating of $1kW$ which converts about $10$ % electrical energy into visible light. If energy other than visible is waste energy. How many kilo-joules does a light bulb wasted in one hour?

• A. 36 kJ
• B. 90 kJ
• C. 3240 kJ
• D. 360 kJ
• E. 32,400 kJ

Answer 1

Answer: (C)

3240 kJ

Given:

$90$ % of electrical energy is wasted in one hour.

The power rating of the bulb is given as $P=1kW$

Energy consumed by the bulb in one hour

$E=Power\times Time=1kW\times 1hr=1kWh$

Using $1kWh=3.6\times {10}^{6}J$

$1kWh=3600$ $kJ$

$\therefore$ Energy wasted

$E_{waste}=0.9\times 3600=3240$ $kJ$