Question

Why an ordinary moving coil ammeter used for d.c., cannot be used to measure a.c.?

Answer 1

Alternating current changes in magnitude and direction and the mean value of ac over a complete cycle is zero. Therefore moving coil ammeter will always read zero when connected in an ac circuit of anyfrequency.This is tthe reason why an ordinary moving coil ammeter used for DC, cannot be used to measure AC.