A galvanometer of resistance 100 Ω shows full-scale deflection at 1 mA. It must be converted into $a_0–10$ A ammeter. Find the necessary shunt resistance.
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Question

A galvanometer of resistance 100 Ω shows full-scale deflection at 1 mA. It must be converted into a 0–10 A ammeter. Find the necessary shunt resistance.

G1 Physics · Accepted Answer

Step 1: Given R(g) = 100 Ω, I(g) = 1 mA = 0.001 A, desired full-scale current I = 10 A. Step 2: A shunt S is placed in parallel with the galvanometer, so both branches have equal voltage. Step 3: I(g)R(g) = (I − I(g))S, therefore S = I(g)R(g)/(I − I(g)). Step 4: S = (0.001 × 100)/(10 − 0.001) = 0.1/9.999 = 0.010001 Ω. Final answer: Approximately 0.01 Ω (Option D).