Question

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?

• A. 17.7 min
• B. 13.7 min
• C. 20.9 min
• D. 14.4 min

Hint:

The heating time of an electric kettle is inversely proportional to the number of turns of the heating coil, as power is proportional to the square of the number of turns.

Answer 1

The Correct Option is D

The heating power of the coil is proportional to the square of the number of turns. Since 10% turns are removed, 90% of the original turns remain, so the time taken to boil the same amount of water increases inversely proportional to the power. Thus, the new time is: \[ \text{New Time} = \frac{16 \times 100}{90} = 14.4 \, \text{min}. \]