JEE MAIN - Physics (2004 - No. 32)
Alternating current can not be measured by $$D.C.$$ ammeter because
Average value of current for complete cycle is zero
$$A.C.$$ Changes direction
$$A.C.$$ can not pass through $$D.C.$$ Ammeter
$$D.C.$$ Ammeter will get damaged.
Forklaring
$$D.C.$$ ammeter measure average current in $$AC$$ current, average current is zero for complete cycle. Hence reading will be zero.