Question

An electric kettle takes $4 \,A$ current at $220 \,V$. How much time will it take to boil $1\, kg$ of water from temperature $20^{\circ} C$ ? The temperature of boiling water is $100^{\circ} C$

• A. 12.6 min
• B. 4.2 min
• C. 6.3 min
• D. 8.4 min

Answer 1

Answer: (C)

Power $= 220\, V \times 4\, A = 880$ watts. $= 880\, J/s. $
Heat needed to raise the temperature of 1 kg water through $80^\circ C $
$ = ms.\Delta T \times 4.2\, J/cal$
$ = 1000\, g \times 1\, cal/g \times 80 \times 4.2\, J/cal.$
$\therefore $ time taken $=\frac{1000\, \times 1 \times 80 \times 4.2}{880} = \frac{336 \times 10^3}{880}$
$ =382\, s=6.3$ min.