Question

A moving coil galvanometer has following characteristics. Number of turns of coil $=80$; Area of coil $=50 \,mm ^{2}$; Resistance of coil $=20\, \Omega$; Flux density of radial field $0.2 \,T$; Torsional constant of suspension wire $=5 \times 10^{-9} N m / rad$. For this moving coil galvanometer, mark the correct statement(s).

• A. The angular deflection produced due to a potential difference of $0.01 mV$ is $0.08$ div.
• B. Current sensitivity of the device is $160 \,div / mA$.
• C. Voltage sensitivity of the device is $8 \,div / mV$.
• D. All of these.

Answer 1

Answer: (D)

Current sensitivity
$I_{S} =\frac{\theta}{I}=\frac{BAN}{k}=\frac{0.2 \times 50 \times 10^{-6} \times 80}{5 \times 10^{-9}} $ div/amp
$=160 \times 10^{3}$ div/amp $=160$ div / mA
Voltage sensitivity, $V_{S}=\frac{\theta}{V}=\frac{B A N}{k R}=\frac{I_{S}}{R}$
$=8 $ div / mV
For $V=0.01 mV , \theta=8 \times 0.01=0.08$ div