It takes 16 min to boil some water in an electric kettle. Due to some defect it becomes necessary to remove 10% turns of heating coil of the kettle. After repairs, how much time will it take to boil the same mass of water ?

14.4 min

We have $\frac{V^2}{R} \times 16=H$        [∵ H = P × t]

$\frac{V^2}{0.9 R} \times t=H \Rightarrow \frac{V^2}{R} \times 16=\frac{V^2}{0.9 R} \times t$

Time, t = 16 × 0.9 = 14.4 min