A coil takes 15 min to boil a certain amount of water, another coil takes 20 min for the same process. Time taken to boil the same amount of water when both coil are connected in series

Options

A. 5 min
B. 8.6 min
C. 35 min
D. 30 min

Answer

C

Explanation

We know that `P = V^(2)/R`
V = constant, `P prop 1/R`……. (i)
`P uarr T darr, P prop 1/T`……. (ii)
By eq. (i) and (ii)
`T prop R`
`R_(1) to 15` min, `R_(2) to 20` min
Then, `(R_(1) +R_(2)) to 35` min