Practice portal › Moving Charges and Magnetism › Moving Coil Galvanometer and its Conversion
Asked in GUJCET 2007 · Conversion to ammeter and voltmeter
Idea: the coil of a galvanometer can carry only a small current I_g, while an ammeter must pass the full line current I.
So most of the current has to be sent around the coil, through a small resistance S joined in parallel with it — the shunt.
Equal potential difference across the two parallel branches gives I_gG=(I-I_g)S, so S=(I_gG)/(I-I_g), which is far smaller than G.
A small parallel resistance also makes the combination's resistance small, which is what an instrument joined in series with a circuit must have.
So a low resistance is connected in parallel with the galvanometer.
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