Question

An immersion heater is rated 418 W. It should heat a litre of water from 10${}^{o}C$ to 30${}^{o}C$ in nearly

• A. 40s
• B. 21s
• C. 24s
• D. 16s

Answer 1

The correct option is B 21s

The rate of heat produced by the heater is given by

$\frac{Q}{t}=ms\Delta \theta$

$t=\frac{Q}{ms\Delta \theta }$

$t=\frac{418}{\left(1\right)\left(1\right)(30-10)}$ ................(s = 1, for water)

$t=\frac{418}{20}$

$t=20.9\approx 21s$