Meters and troubleshootingQuestion 1172 of 1506

Why does a basic permanent-magnet moving-coil meter not work correctly on AC?

The coil resistance is far too high for AC.
The needle tries to change direction on each half-cycle.
The magnet is too weak.
The scale is not marked in AC units.

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Correct answer: The needle tries to change direction on each half-cycle.

A PMMC movement is sensitive to polarity, so the needle flutters on AC unless the AC is first rectified.

Source: Lessons in Electric Circuits II: AC (Kuphaldt), 12.1: AC Voltmeters and Ammeters

Questions last reviewed: 18 October 2026

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