Question

Water in an electric kettle connected to a 220 V supply takes 5 minutes to reach its boiling point. How long will it take if the supply voltage falls to 200 V?

Answer 1

Given,

Voltage supplied = 220 V

Time taken is = 5 min

In second situation

Voltage supplied = 200 v

We have to find the time taken

We know,

$Heat=\frac{V^2}{R}\times t$

The heat required to boil the water in both cases will be the same.

So, $\frac{V_1^2}{R}\times t_1=\frac{V_2^2}{R}\times t_2\Rightarrow {220}^2\times 5={200}^2\times t_2\Rightarrow t_2=6.05mins$

Hence in second case the time required is 6.05 min.