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
Verified Correct Answer: E.
Physical Principles & Numerical Solution
D ∝ l2
E will increase 4 times when current is doubled.
Therefore time will decrease by a factor of 4, which is 1 minute.
Source: Myschool Past Questions Archive (Record #21258)