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Asked in GSEB Board March 2020 · Galvanometer sensitivity and figure of merit
Idea: at the steady deflection the magnetic torque on the coil is balanced by the restoring torque of the suspension: NIAB=kφ, where k is the torsional constant.
Rearranging, φ/I=(NAB)/k, and that ratio is what current sensitivity means — the deflection produced per unit current.
N, A and B all sit on top; only k is underneath.
So the current sensitivity is inversely proportional to the torsional constant: a slacker suspension, with a smaller k, makes a more sensitive galvanometer.
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