First slide

Electrical power

Question

An electric kettle takes 4 A current at 220 V. How much time will it take to boil 1 kg of water from room temperature 20⁰C? The temperature of boiling water is

Moderate

A

6.4 minutes
B

6.3 minutes
C

12.6 minutes
D

12.8 minutes

Solution

Electric power consumed by kettle, P = 220 x 4 W
Heat required,
$\begin{array}{l} H = 1000 \times 1 (100 - 20) = 1000 \times 80 cal \\ = 4200 \times 80 J \\ P = \frac{H}{t} \Rightarrow H = P \times t \\ ∴ 220 \times 4 \times t = 4200 \times 80 \Rightarrow T = 6 .3 minutes \end{array}$

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