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A galvanometer of coil resistance G is converted into an ammeter using a shunt of resistance S. Its figure of merit is K (current per division) and it shows n divisions of deflection. What is the total current I flowing in the circuit?

1. KS/(S+G)
2. (G+S)/(nKS)
3. nKS/(G+S)
4. nK(G+S)/S

Correct answer: nK(G+S)/S

Solution

The coil current is nK; using the shunt current-divider relation, the total current scales up by (G+S)/S.

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