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In a circuit, a non-ideal ammeter reads 4 A and a non-ideal voltmeter reads 20 V across a resistor R. Taking meter non-idealities into account, the actual value of R is:

1. greater than 5 ohm
2. exactly 5 ohm
3. less than 5 ohm
4. between 4 ohm and 5 ohm

Correct answer: greater than 5 ohm

Solution

With the standard 'ammeter measures both R-current and voltmeter-current' connection, the ammeter overreads the current through R, so the true resistance is greater than the apparent 20/4 = 5 ohm.

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