(a) Water boils in an electric kettle in `15` minutes after being swiched on. Using the same mains supply, should the length of the heating element be increased or decreased if the water is to boiled in `10` minutes ? Why ?
Does Ohm's law hold good under all conditions ?

Explanation

(a) The rate of heat production `(V^2//R)` is inversely proportional to `R`. Thus, to boil water in `10` minutes, the resistance of the element should be `(10//15) R, i.e., (2//3) R`. This is possible only if the length of the wire is decreased to `(2//3)` of its initial value.
(b) N/A.