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Two batteries, one of emf 18 volt and internal resistance 2Ω and the other of emf 12 volt and internal resistance 1Ω, are connected as shown. The voltmeter V will record a reading of

1. 30 volt
2. 18 volt
3. 15 volt
4. 14 volt

Correct answer: 15 volt

Solution

The two batteries are connected in series, but their emfs oppose each other. The net emf is 18V - 12V = 6V. The total internal resistance is 2Ω + 1Ω = 3Ω. Since no external resistance is mentioned, the voltmeter will measure the potential difference across the 12V battery, which is 15V (12V + current × 1Ω).

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