A student boils the water in an electric kettle for 20 minutes after being switched on. If the boiling time is to be decreased then the length of the heating element should be [[1]].

The student should decrease the length of the heating element to decrease the boiling time.
By Ohm’s law of heating, the heat produced is given as

H = I^{2} Rt

,
But it is known that the current is given as

I = V / R

Hence the equation for the heat produced can also be written as

H = \frac{V^{2} t}{R}

Since, the heat required is the same in both cases, it can be stated that

\frac{V^{2} t_{1}}{R_{1}} = \frac{V^{2} t_{2}}{R_{2}}

or it can be written as

\frac{t_{1}}{t_{2}} = \frac{R_{1}}{R_{2}}

From the above relation, for t2 to be less than t1, R2 should be lesser than R1 if we want the water to boil quicker.

A student boils the water in an electric kettle for $20 minutes$ after being switched on. If the boiling time is to be decreased then the length of the heating element should be [[1]].