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The figure below shows a circuit for an AC voltmeter. It utilizes a moving-coil meter that gives a full-scale reading when the average current flowing through it is 1 mA. The moving-coil meter has a 50-Ω resistance. The value of R that results in the meter indicating a full-scale reading when the input sine-wave voltage VI is 20 V peak-to-peak is

The figure below shows a circuit for an AC voltmeter. It utilizes a moving-coil meter that gives a full-scale reading when the average current flowing through it is 1 mA. The moving-coil meter has a 50-Ω resistance. The value of R that results in the meter indicating a full-scale reading when the input sine-wave voltage VI is 20 V peak-to-peak is Correct Answer 3.133 kΩ

Average value of input voltage= 20/π or 6.366 V. Since there is diode half of the time there is no voltage across the voltmeter hence the average value of the input voltage is 10/π or 3.183V. The total resistance required to generate 1mA current is 3.183 kΩ out of which 50Ω is provided by the moving coil. Therefore, a resistance of 3.133 kΩ is required.

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