Question:
A galvanometer having a resistance of \(20\ \Omega\) and 30 divisions on both sides has figure of merit 0.005 ampere/division. The resistance that should be connected in series such that it can be used as a voltmeter upto 15 volt, is:
A galvanometer having a resistance of \(20\ \Omega\) and 30 divisions on both sides has figure of merit 0.005 ampere/division. The resistance that should be connected in series such that it can be used as a voltmeter upto 15 volt, is:
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Full-scale current is (divisions) x (figure of merit); the total resistance must be \(V/I_g\), and the series resistance is that minus \(G\).
Updated On: Nov 5, 2026
- \(120\ \Omega\)
- \(125\ \Omega\)
- \(80\ \Omega\)
- \(100\ \Omega\)
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The Correct Option is C
Solution and Explanation
Full-scale deflection current: \(I_g = 30\times0.005 = 0.15\ \mathrm{A}\).
For a 15 V voltmeter: \(I_g(G + R) = 15\), so \(G + R = \frac{15}{0.15} = 100\ \Omega\).
\(R = 100 - 20 = 80\ \Omega\).
Answer: (3) \(80\ \Omega\)
For a 15 V voltmeter: \(I_g(G + R) = 15\), so \(G + R = \frac{15}{0.15} = 100\ \Omega\).
\(R = 100 - 20 = 80\ \Omega\).
Answer: (3) \(80\ \Omega\)
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