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(B) standard $DC$ voltmeter cannot measure $AC$ voltage because the average value of an alternating voltage over a full cycle is zero, causing the ins

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hot wire voltmeter

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(B) standard $DC$ voltmeter cannot measure $AC$ voltage because the average value of an alternating voltage over a full cycle is zero, causing the instrument to show a zero reading.To measure $AC$ voltage, we use an instrument that operates on the heating effect of current, which is independent of the direction of the current.A hot wire voltmeter works on the principle of the heating effect of current $(H = I^2Rt)$, where the deflection is proportional to the square of the current (or voltage). Therefore, it can measure the $RMS$ value of $AC$ voltage.

The $AC$ voltage across a resistance can be measured using a

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