An electric kettle takes 4A current at 220V. Then the time it will take to boil 1 kg of water from temperature 20°C is 

Given that electric kettle v = 220 V, I = 4 A
Heat required to boil 1 kg of water = VIt
$\begin{array}{l}\mathrm{ms\Delta t}+\mathrm{mL}=\mathrm{vIt}\\ 1\times 4200\times 80+540\times 200=4\times 220\times \mathrm{t}\\ \Rightarrow 4200\left(620\right)=4\times 220\times \mathrm{t}\\ \therefore \mathrm{t}=\frac{4200\times 620}{4\times 220}\\ \mathrm{t}=49\min \end{array}$