Question

An electric kettle takes $4A$ current at $220V$. How much time will it take to boil $1kg$ 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 $=220V\times 4A=880$ watts. $=880J/s.$
Heat needed to raise the temperature of 1 kg water through $80^{\circ }C$
$=ms.\Delta T\times 4.2J/cal$
$=1000g\times 1cal/g\times 80\times 4.2J/cal.$
$\therefore$ time taken $=\frac{1000\times 1\times 80\times 4.2}{880}=\frac{336\times 10^3}{880}$
$=382s=6.3$ min.