A cell of emf 90 V is connected across series combination of two resistors each of 100Ω resistance. A voltmeter of resistance 400Ω is used to measure the potential difference across each resistor. The reading of the voltmeter will be :
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Question

A cell of emf 90 V is connected across series combination of two resistors each of 100Ω resistance. A voltmeter of resistance 400Ω is used to measure the potential difference across each resistor. The reading of the voltmeter will be :

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G1 Physics · Accepted Answer

The voltmeter is connected across one 100 Ω resistor, so their parallel equivalent is (400×100)/(400+100) = 80 Ω. Total resistance = 80 + 100 = 180 Ω. Circuit current = 90/180 = 0.5 A. Potential across the parallel branch, and hence voltmeter reading, is 0.5×80 = 40 V.