Question

A heater of 220 V boils a volume of water in 5 minute time. If the heater is operated at 110 V, the same volume of water will boil in

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

Answer 1

Answer: (D)

20 min

Heat generated by a heater with resistance value R is given by,
$H=Pt=\frac{V^2}{R}t$
Now the water has to be boiled to the same temperature so we have to give same amount of heat.
Therefore, for value of voltage 220V and 110V we can write eq for heat generated i.e.

$\frac{{220}^2}{R}5$ = $\frac{{110}^2}{R}t$

$t=20$ minutes