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  4. In the circuit figure, the voltmeter reads 30 V . The resistance of the voltmeter is <img class=img-fluid question-image alt=Question src=https://cdn.tardigrade.in/q/nta/p-bgcpkm582xd5.png />

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Q. In the circuit figure, the voltmeter reads $30 \, V$ . The resistance of the voltmeter is

Question

NTA AbhyasNTA Abhyas 2020Current Electricity

Solution:

The potential difference across $300 \, \Omega =60-30=30V$
Therefore the effective resistance of voltmeter resistance $R$ and $400 \, \Omega $ in parallel will be equal to $300 \, \Omega $ , as 60 V is equally divided between two parts.
So, 300 $=\frac{R \times 400}{R + 400}$
or $300R \, +120000=400R \, or \, R=1200 \, \Omega $