In an electric kettle water boils in 10 m minutes. It is required to boil the boiler in 15 minutes, using same supply mains

Answer: Option A

Power dissipated in a heating element is given by: P = V² / R, where V is the supply voltage (constant from mains) and R is the resistance of the heating element.

Heat produced is proportional to power × time. To boil the same quantity of water in more time (15 minutes instead of 10 minutes), the heating element must supply less power.

Since V is constant, to reduce power, the resistance R of the element must be increased.

Resistance of a wire is proportional to its length (R ∝ L). Therefore, to increase resistance, the length of the heating element should be increased.

Final Answer: Length of heating element should be increased (Option B)