A multirange current meter can be constructed by using a galvanom… - Vidyadip

Question

A multirange current meter can be constructed by using a galvanometer circuit as shown in Fig. We want a current meter that can measure 10mA, 100mA and 1A using a galvanometer of resistance 10Ω and that prduces maximum deflection for current of 1mA. Find S₁, S₂ and S₃ that have to be used.

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Answer

Key concept: A galvanometer can be converted into ammeter by connecting a very low resistance wire (shunt S) connected in parallel with galvanometer. The relationship is given by I_gG = (l - I_g) S, where I_g is the range of galvanometer, G is the resistance of galvanometer.

For measuring I₁ = 10mA : IG.G = (I₁ - IG)(S₁ + S₂ + S₃)

For measuring I₂ = 100mA : IG(G + S₁) = (I₂ - IG)(S₂ - S₃)

For measuring I₃ = 1A : IG(G + S₁ + S₂) =(I₃ - IG)(S₃)

Gives S₁ = 1Ω, S₂ = 0.1Ω and S₃ = 0.01Ω.

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