A moving-coil galvanometer has resistance 30 Ω and gives full-scale deflection at 20 mA. It is converted into a 3 A ammeter using a shunt resistance S. The approximate value of S is:
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A moving-coil galvanometer has resistance 30 Ω and gives full-scale deflection at 20 mA. It is converted into a 3 A ammeter using a shunt resistance S. The approximate value of S is:

G1 Physics · Accepted Answer

At full scale, voltage across galvanometer equals voltage across shunt: I g G = ( I − I g ) S . I_gG=(I-I_g)S. I g ​ G = ( I − I g ​ ) S . Thus S=(0.020×30)/(3-0.020)≈0.201 Ω≈0.2 Ω.