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

Explanation

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`