Question

A moving coil galvanometer has the following characteristics – Number of turns of coil = 50; Area of coil = 70 mm^2; Resistance of coil = 30 Ω; Flux density of radial field = 0.1 T; Torsional constant of suspension wire = 7 × 10^-8 N m/rad. Calculate the current and voltage sensitivity.

(a) 10 div/mA, 0.166 div/mV

(b) 15 div/mA, 0.115 div/mV

(c) 5 div/mA, 0.167 div/mV

(d) 20 div/mA, 0.100 div/mV

I had been asked this question during an interview.

The origin of the question is Moving Coil Galvanometer in division Moving Charges and Magnetism of Physics – Class 12

Answer 1

The correct answer is (c) 5 div/mA, 0.167 div/mV

To explain: N = 50; A = 70 mm^2; B = 0.1 T; k = 7 × 10^-8 N m/rad; R = 30 Ω

Current sensitivity (IS) = \(\frac {NAB}{k}\) = 50 × 70 × 10^-6 × \(\frac {0.1}{7}\) × 10^-8

= 350 × \(\frac {100}{7}\) = 5 × 10^3 div/amp

= 5 div/mA

Voltage sensitivity (VS) = \(\frac {NAB}{kR} = \frac {I_S}{R}\)

= \(\frac {5}{30} = \frac {1}{6}\)

= 0.167 div/mV