The self-inductance of a choke coil is `10mH`. When it is connected with a `10 V DC` source, then the loss of power is `20 "watt"`. When it is connected with `10 "volt" AC` source loss of power is `10"watt"`. The frequency of `AC` source will be

Options

A. 50 Hz
B. 60 Hz
C. 80 Hz
D. 100 Hz

Answer

C

Explanation

For dc ` P = (V^(2))/(R) rArr R - ((10)^(2))/(20) = 5 Omega `
For ac `P = (V_(rms)^(2) R)/(Z^(2)) rArr Z^(2) = (10^(2)xx 5)/( 10) = 50 Omega^(2)`
`:. Z^(2) = R^(2) + 4 pi ^(2) f^(2) L^(2)`
`rArr f = 80 Hz`