Question

You have the following appliances each of $500W$ running on $220V$ a.c.:

(1) Electric iron.

(2) Electric lamp.

(3) Electric room heater.

The electric resistance is:

• A. maximum for the heater.
• B. maximum for the electric lamp.
• C. maximum for the electric iron.
• D. same in all the three cases.

Answer 1

The correct option is D same in all the three cases.

Power is defined as, $P=\frac{V^2}{R}$, where $V$ is voltage rating and $R$ is the resistance rating

Hence,

Resistance$,R=\frac{V^2}{P}=\frac{(220{)}^2}{P}$. Since $P$ of each appliance is the same, hence $R$ is same for all the three appliances.