Moving Coil Ammeter/Voltmeter – Rankers Physics

Average Current and RMS Current: Practice Problem & Solution

Assertion (A): The moving coil ammeters or voltmeters can't be employed to measure alternating current or voltage respectively. Reason (R): If an alternating current is passed through a moving coil ammeter or voltmeter, then the average value of torque experienced by the coil is zero.  
Both (A) & (R) are true and the (R) is the correct explanation of the (A)
Both (A) & (R) are true but the (R) is not the correct explanation of the (A)
(A) is true but (R) is false
Both (A) and (R) are false

Solution Explained:

To solve this problem, we apply the core principles of Average Current and RMS Current. Understanding the underlying formula is key to arriving at the correct answer below:

Moving coil instruments measure the average value of current. For AC, the average value over a full cycle is zero, resulting in zero average torque. Hence, moving coil ammeters/voltmeters cannot measure AC. Both assertion and reason are true, and the reason correctly explains the assertion.

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