The self inductance of a choke coil is 10 mH. When it is conected with a 10V D.C. source, then the loss of power is 20 watt. When it is connected with 10 volt A.C. source loss of power is 10 watt. The frequency of A.C. source will be-
(A) 50 Hz
(B) 60 Hz
(C) 80 Hz
(D) 100 Hz