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A galvanometer has a coil of resistance 100 ohm and gives a full-scale deflection for 30 mA current. It is to work as a voltmeter of 30 volt range, the resistance required to be added will be
- 900 Ω
- 1800 Ω
- 500 Ω
- 1000 Ω
Correct answer: 1800 Ω
Solution
To convert the galvanometer into a voltmeter, a series resistance is added. The total resistance required for the 30 V range is R_total = V/I = 30/0.03 = 1000 Ω. Since the galvanometer already has a resistance of 100 Ω, the additional resistance needed is R = R_total - R_g = 1000 - 100 = 900 Ω.
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