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A galvanometer shows a deflection of 50 divisions without shunt. When a 12 Ω shunt is connected across it, the deflection reduces to 20 divisions. What is the resistance of the galvanometer?

1. 18 Ω
2. 36 Ω
3. 24 Ω
4. 30 Ω

Correct answer: 18 Ω

Solution

Deflection is proportional to galvanometer current. With shunt, Ig = (20/50)I = 0.4I and shunt current Is = 0.6I. Equating voltages: 0.4I*G = 0.6I*12, so G = (0.6*12)/0.4 = 18 ohm.

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