JEE Main 2024 Physics question
Water boils in an electric kettle in 20 minutes after being switched on. Using the same main supply, the length of the heating element should be ………….. to …………. times of its initial length if the water is to be boiled in 15 minutes.
Answer: (C)
Solution
Heat = V²t/R is fixed, so t ∝ R ∝ L. For 15 min instead of 20 min, L′ = (15/20)L = (3/4)L: decreased to 3/4.