How long will it take to boil same quantity of water using the same heating coil but with the current doubled?

It takes 4 minutes to boil a quantity of water electrically. How long will it take to boil same quantity of water using the same heating coil but with the current doubled? (neglecting any external heat loss).

A. 64 minutes
B. 32 minutes
C. 8 minutes
D. 2 minutes
E. 1 minute

Correct Answer:

Option E = 1 minute

Explanation

D ∝ l²

E will increase 4 times when current is doubled.
Therefore time will decrease by a factor of 4, which is 1 minute.