Question

A heater of 220 V heat a volume of water in 5 minute time. A heater of 110 V heats the same volume of water in

• A. 5 minutes
• B. 8 minutes
• C. 10 minutes
• D. 20 minutes

Answer 1

The correct option is D 20 minutes

Heat produced, $H=\frac{V^2}{R}t$
As same volume of water heat so heat produced and resistance will be constant.
Thus, $V^2\propto \frac{1}{t}$
Here, $\frac{V_2^2}{V_1^2}=\frac{t_1}{t_2}$
$\Rightarrow t_2=\frac{V_1^2}{V_2^2}{t}_1=\frac{{220}^2}{{110}^2}\times 5=20min$