Question

An immersion heater is rated $836W$. It should heat $1l$ of water from ${20}^0$C to ${40}^0$C in about:

• A. $200s$
• B. $100s$
• C. $836s$
• D. $418s$

Answer 1

The correct option is B $100s$

Useful data:

Specific heat capacity of water $s=4.186J/gK$
Density of water $\rho =1000g/l$

Volume of water $V=1l$
Heat developed in a body is given by:
$Q=ms\Delta T$

$Q=\rho Vs\Delta T$
From definition of power,

$P=Q/t$ where $t:$ time of heating

$t=\frac{Q}{P}$

$t=\frac{1000\times 1\times 4.186\times 20}{836}$
$t=100s$