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The figure shows a source (a battery) wi...

The figure shows a source (a battery) with an emf E of 12 V with an internal resistance r of `2Omega` and an external resistance of `4Omega` is added to complete the circuit. What are the voltmeter and ammeter readings

Text Solution

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AN ideal voltmeter has infinite resistance, hence no current flows through it. An ideal ammeter has zero resistance. The current i through the resistor
`i=(E)/(R+r)=(12)/(4+2)=2A`
The ammeter will read `i = 2 A` As there is no potential difference between points a and p or between points band , i.e. `V_(ab) = V_(pg)`, we can find Vab by considering a and b either as the terminals of the resistor or as the terminals of the source.
`V_(ab) = iR = 2 xx 4 = 8V`
Considering them as the terminals of the source, we have
`V_(ab)= E - ir = 12 - 2 xx 2 = 8V` Either way, we conclude that the voltmeter reads `V_(ab)= 8 V`
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