An electric kettle has tow heating coils. When one of the coils connected to an AC source, the water in the kettle boils in `10` min. when the other coil is used the water boils in `40` min. if both the coils are connected in parallel, the time taken by the same quantity of water of boil will be

Options

A. 8 min
B. 4 min
C. 25 min
D. 15min

Explanation

`Q=(V^(2))/(R_(1))xxt_(1)=(V^(2))/(R_(2))xxt_(2)=(V^(2))/(R)xxt`
`(1)/(R)=(1)/(R_(1))+(1)/(R^(2))rArr(Q)/(V^(2)t)=(Q)/(V^(2)t_(1))+(Q)/(V^(2)t_(2))`
`rArr (1)/(t)=(1)/(t_(1))+(1)/(t_(2))rArrt=(t_(1)t_(2))/(t_(1)+t_(2))=(10xx40)/(10+40)`
=98 min.