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A galvanometer has a resistance of 50 Ω and a scale of 25 divisions. If a current of 4 × 10⁻⁴ A produces a deflection of one division, what resistance should be added in series to use it as a voltmeter of 25 V range?

1. 2450 Ω in series
2. 2500 Ω in series
3. 245 Ω in series
4. 2550 Ω in series

Correct answer: 2450 Ω in series

Solution

Ig = 25 * 4e-4 = 0.01 A. Series resistance R = V/Ig - G = 25/0.01 - 50 = 2500 - 50 = 2450 ohm.

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