T/4??from where this come

Frequency of A.C., n = 50 Hz time period T = Time in which current changes from peak value (i) to zero (i) = 40 50 200S 300 1 S. 50 n 1 1 1 200 i.e., AT = S. then Ai = change in current e - 0 -1 =-1 A. mean induced e.m.f., Ai At e =-M- =-1.5 -1 = 300 V. 1/200