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Question
A moving coil galvanometer has been fitted with a rectangular coil having 50 turns and dimensions 5 cm × 3 cm. The radial magnetic field in which the coil is suspended is of 0.05 Wb/m2. The torsional constant of the spring is 1.5 × 10−9 Nm/degree. Obtain the current required to be passed through the galvanometer so as to produce a deflection of 30°.
Solution
N = 50 turns, C = 1.5 × 10−9 Nm/degree, A = lb = 5 cm × 3 cm = 15 cm2 = 15 × 10-4 m2 , B = 0.05 Wb/m2 , θ = 30°
NIAB=Cθ
∴ The current through the coil, I = `("C"theta)/"NAB"`
`= (1.5 xx 10^-9 xx 30)/(50 xx 15 xx 10^-4 xx 0.05) = (3 xx 10^-5)/(5 xx 0.5) = 1.2 xx 10^-5 "A"`
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