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A galvanometer of 50 ohm resistance has 25 divisions. A current of 4 × 10⁻⁴ ampere gives a deflection of one per division. To convert this galvanometer into a voltmeter having a range of 25 volts, it should be connected with a resistance of
- 2450 Ω in series
- 2500 Ω in series
- 245 Ω in series
- 2550 Ω in series
Correct answer: 2450 Ω in series
Solution
The full-scale deflection current is 25 × 4 × 10⁻⁴ A = 0.01 A. To convert the galvanometer into a voltmeter with a range of 25 V, the series resistance required is R = (V/I) - G = (25/0.01) - 50 = 2450 Ω.
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