An electric bulb rated for `500 W` at `100 V` is used in a circuit having a `200 V` supply. The reistance `R` that must be put in series with bulb, so that the bulb delivers `500 `W is ……….`Omega`.

Options

A. `18 Omega`
B. `20 Omega`
C. ` 40 Omega`
D. `700 Omega`

Answer

B

Explanation

`P = VI or I = (P)/( V) or I = ( 500 W)/( 100 V) = 5 A`
Now, ` 5 R = 100 or R = 20 Omega`