Question:
A moving coil galvanometer allows a full scale current of \(10^{-4}\) A. A series resistance of 2 M\(\Omega\) is required to convert the above galvanometer into a voltmeter of range 0-5 V. Therefore the value of shunt resistance required to convert the above galvanometer into an ammeter of range 0.10 mA is :
A moving coil galvanometer allows a full scale current of \(10^{-4}\) A. A series resistance of 2 M\(\Omega\) is required to convert the above galvanometer into a voltmeter of range 0-5 V. Therefore the value of shunt resistance required to convert the above galvanometer into an ammeter of range 0.10 mA is :
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For the voltmeter, \(G+R_s=V/I_g\); with the given numbers this does not give a positive G, and an ammeter range equal to \(I_g\) needs no finite shunt.
Updated On: Nov 5, 2026
- \(200\ \Omega\)
- \(500\ \Omega\)
- \(100\ \Omega\)
- None of the options are correct
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The Correct Option is D
Solution and Explanation
Voltmeter conversion: \(V=I_g(G+R_s)\Rightarrow G+R_s=\dfrac{5}{10^{-4}}=5\times10^{4}\,\Omega\).
With \(R_s=2\ \mathrm{M}\Omega=2\times10^{6}\,\Omega\) this would give \(G=5\times10^4-2\times10^6\lt 0\), which is impossible, so the data are inconsistent.
Ammeter conversion: the required range 0.10 mA \(=10^{-4}\) A equals the full-scale current \(I_g\), so the shunt \(S=\dfrac{I_gG}{I-I_g}\to\infty\); no finite shunt resistance of 200, 500 or 100 \(\Omega\) can give this.
Hence none of the listed values is correct.
Answer: (4) None of the options are correct
With \(R_s=2\ \mathrm{M}\Omega=2\times10^{6}\,\Omega\) this would give \(G=5\times10^4-2\times10^6\lt 0\), which is impossible, so the data are inconsistent.
Ammeter conversion: the required range 0.10 mA \(=10^{-4}\) A equals the full-scale current \(I_g\), so the shunt \(S=\dfrac{I_gG}{I-I_g}\to\infty\); no finite shunt resistance of 200, 500 or 100 \(\Omega\) can give this.
Hence none of the listed values is correct.
Answer: (4) None of the options are correct
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