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Ammeter-Voltmeter Method

The resistance of a coil is measured by the ammeter-voltmeter method. With the voltmeter connected across the coil, the readings on the ammeter and voltmeter are 0.4A and 3.2 V respectively. The resistance of the voltmeter is 500 Ohm. Calculate (a) the true value of the resistance and (b) the percentage error in the value of the resistance, if the voltmeter current were neglected.

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Solution Preview

An unknown resistance can be determined by means of the Voltmeter-Ammeter method. This method works on the Ohm's law as follows:

As per Ohm's law, the current I flowing through a resistance R, through which a voltage V is applied, is thus given by: I = V/R or R = V/I (Equation 1)

A known voltage is applied across unknown resistance and the current flowing through the resistance is measured. To measure the voltage and current, a voltmeter and an ammeter are connected in the circuit. Then, using equation (1), the value of the unknown resistance R is calculated.

There are two different ways the voltmeter ...

Solution Summary

Ammeter-voltmeter methods are examined. The percentage errors in the value of the resistance are provided.