Alternating current cannot be measured with a moving coil galvanometer directly because
Correct answer: B. the deflection reverses every half cycle and the pointer cannot follow, so it averages to zero
- A. the current is too large
- B. the deflection reverses every half cycle and the pointer cannot follow, so it averages to zero
- C. the galvanometer has no coil
- D. AC does not flow through a galvanometer
Explanation
The torque reverses with the current, and at 50 Hz the inertia of the pointer prevents it from following, so it simply sits at zero. Measuring AC therefore requires either a rectifier ahead of the meter or an instrument such as a hot wire ammeter that responds to the heating effect, which does not depend on direction. This is why hot wire meters read rms values directly.
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About Phase of Alternating Current
Phase describes the position of an alternating voltage or current within its cycle and the phase difference between two sinusoidal quantities. The topic covers in phase signals, phase angle and lead or lag in resistive, inductive and capacitive circuits, rather than the amplitude or frequency of the supply.
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