Q. An electric kettle takes $4A$ current at $220\ V.$ How much time will it take to boil 1 kg of water from temperature $20℃?$ The temperature of boiling water is $100℃$
A) $12.6\ \min$
B) 4.2 min
C) 6.3 min
D) 8.4 min
Explanation
(c) $P \times t = mc\mathrm{\Delta}\theta$
$\Rightarrow t = \frac{mc\mathrm{\Delta}\theta}{P} = \frac{4200\ m\mathrm{\Delta}\theta}{P} = \frac{4200 \times m \times \mathrm{\Delta}\theta}{VI}$
$\left\{ \because C_{water} = 4200\frac{J}{kg \times ℃} \right\}$
$\Rightarrow t = \frac{4200 \times 1 \times (100 - 20)}{220 \times 4} = 381\sec \approx 6.3\ \min$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.