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In the circuit diagrams (A, B, C and D) shown below, R is a high resistance and S is a resistance of the order of galvanometer resistance G. The correct circuit, corresponding to the half deflection method for finding the resistance and figure of merit of the galvanometer, is the circuit labelled as:

Asked in JEE Main Online 2014 · Galvanometer sensitivity and figure of merit

• (1) Circuit A with G = (RS)/(R - S)
• (2) Circuit B with G = S
• (3) Circuit C with G = S
• (4) Circuit D with G = (RS)/(R - S)

Step-by-step solution

Why the other options are wrong

• (1) Picks the circuit where the high resistance R is across G and S is in series, i.e. the roles are swapped.
• (2) Picks a circuit with S in series with G, which is not a shunt.
• (3) Picks a circuit where K₂ shorts out R, so R and S are simply in series with G; no shunt is ever placed across G.

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