Q. An electric water kettle rated 2.1 kW is filled with 1.5 kg of water at $20{^\circ}C.$ How many seconds does it take to reach the boiling point of water? Assume that there are no heat losses from the kettle. Specific heat capacity of water is $4200\ {Jkg}^{- 1}\ K^{- 1}$
A) 60
B) 120
C) 240
D) 480
Explanation
(c) $\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ P \times t = ms\ \mathrm{\Delta}t$
$\Rightarrow \ 2.1 \times 10^{3} \times t$
$= 1.5 \times 4200 \times \left\lbrack (100 + 273) - (20 + 273) \right\rbrack$
$\Rightarrow \ \ \ \ \ = \frac{1.5 \times 4200 \times 80}{2.1 \times 10^{3}} = 240s$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.