When three identical bulbs of `60 W, 200 V` rating are connected in series to a `200 V` supply, the power drawn by them will be

Options

A. `60 W`
B. `180 W`
C. `10 W`
D. `20 W`

Answer

D

Explanation

(d) Let `R_(1), R_(2)` and `R_(3)` are the resistance of three bulbs respectively.
In series order,
`R = R_(1) + R_(2) + R_(3)`
but `R = V_(2)//P` and supply voltage in series order is the same as the rated voltage.
`:. (V^(2))/(P) = (V^(2))/(P_(1)) + (V^(2))/(P_(2)) + (V^(2))/(P_(3))`
or `(1)/(P) = (1)/(60) + (1)/(60) + (1)/(60)`
or `P = (60)/(3) = W`