question_answer

A heating coil is used to heat water in a container from \[15{}^\circ C\] to \[50{}^\circ C\] in\[20\text{ }mm\]. Two such coils are then joined in series to heat the same amount of water for the same temperature difference from the same constant voltage source. The time taken now is:

A)  \[5\,\min \]                               

B)  \[10\,\min \]

C)  \[20\,\min \]                             

D)  \[40\,\min \]