Question

The AC voltage across a resistance can be measured using a

A)moving magnet galvanometer

B)moving coil galvanometer



C)hot wire voltmeter



D)potentiometer

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Answer 1

ANSWER

c)hot wire

SOLUTION

Ordinary DC voltmeter cannot measures alternating voltages. When used in AC circuits, these instruments record zero reading because average value of alternating voltage over a full cycle is zero. Alternating voltage across the resistance can be measured by using an AC voltmeter. Such an AC voltmeter is known as a hot wire voltmeter which measure only virtual values(r.m.s values) of the alternating voltages. Moving coil or magnet galvanometer can measure only DC values. When AC passes through a galvanometer it will not show any deflection, because the impulses to the moving parts of the galvanometer are equal and opposite. To measure AC, the heating effect of current is used because heating effect does not depend on the direction of flow of current. The hot wire voltmeter work on the principle of heating effect of current.