An electric bulb marked 40 W and 200 V is used in a circuit of supply voltage 100 V. Now its power is .... .

Options

A. 10 W
B. 20 W
C. 40 W
D. 100 W

Answer

A

Explanation

10 W
P = `(V^(2))/(R) ` , where R is constant (bulb is same )
P `prop V^(2)`
`therefore (P_(2))/(P_(1)) = ((V_(2))/(V_(1)))^(2)`
`therefore P_(2) = P_(1) xx ((V_(2))/(V_(1)))^(2)`
= ` 40 xx ((100)/(200))^(2) = 40 xx (1)/(4) = 10` W