A moving coil galvanometer of resistance 100 Ω shows a full scale deflection for a current of 1 mA. The value of resistance required to convert this galvanometer into an ammeter, showing full scale deflection for a current of 5 mA, i $s _____$ Ω
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Question

A moving coil galvanometer of resistance 100 Ω shows a full scale deflection for a current of 1 mA. The value of resistance required to convert this galvanometer into an ammeter, showing full scale deflection for a current of 5 mA, i $s _____$ Ω

Options

G1 Physics · Accepted Answer

Galvanometer resistance: G = 100 Ω. Full-scale galvanometer current: I(g) = 1 mA. Required ammeter full-scale current: I = 5 mA. Therefore the shunt current is I(s) = I-I(g) = 4 mA. The galvanometer and shunt are in parallel, so their potential differences are equal: I(g)G = I(s)S. Hence, S = I(g)G/I(s) = (1×100)/4 = 25 Ω. Correct option: A.

A moving coil galvanometer of resistance 100 Ω shows a full scale deflection for a current of 1 mA. The value of resistance required to convert this galvanometer into an ammeter, showing full scale deflection for a current of 5 mA, i s _____ Ω