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 ${20}^o$C? (the temperature of boiling water is ${100}^o$C).

• A. $12.6$min
• B. $12.8$min
• C. $6.3$min
• D. $6.4$min

Answer 1

Answer: (C)

$6.3$min

Given : $m=1kg=1000g$

Specific heat capacity of water $S=1cal/g{.}^{o}C$

Heat required, $Q=mS\left(\Delta T\right)=1000\times 1\times (100-20)$
$Q=1000\times 80$cal .......(1)
Heat produced in time t is, $H=VIt$
$H=220\times 4\times t$ Joule
$H=\frac{220\times 4\times t}{4.18}$Cal ......(2)
Equating (1) and (2),

$\therefore \frac{220\times 4\times t}{4.18}=1000\times 80$
$\Rightarrow t=\frac{1000\times 80\times 4.18}{220\times 4}=380s=6.3$min.