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Shunt wire should be ______.

Asked in GUJCET 2019; GUJCET 2022 · Conversion to ammeter and voltmeter

(1) Thick and long
(2) Thick and short
(3) Thin and long
(4) Thin and short

Answer: (2) Thick and short

Step-by-step solution

Idea: a shunt is a small resistance joined in parallel with the galvanometer so that most of the current goes through the shunt and only a known small fraction through the coil.

For a wire, R=(ρℓ)/A.

Making it short cuts ℓ; making it thick raises A. Both push R down.

So the shunt wire should be thick and short.

Why the other options are wrong

(1) Thick is right, long is not: R=(ρℓ)/A grows with length, and the shunt has to be the low-resistance path so that nearly all the current bypasses the galvanometer.
(3) Both halves are wrong. A thin, long wire has the largest (ρℓ)/A of the four, so it would push current through the galvanometer instead of around it.
(4) Short is right, thin is not: a small cross-section A raises R=(ρℓ)/A, and a thin wire would also overheat while carrying the bulk of the current.

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