Question

A moving coil galvanometer has following characteristics,
Number of turns = $80$, Area of coil =$50{\text{mm}}^2$, Resistance of coil = $20\Omega$, magnetic field = $0.2\text{T}$, torsional constant of the suspension wire = $5\times {10}^{-9}\text{N-m/rad}$.
Which of the following statements are correct.

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

Answer 1

The correct option is B All of the above.

We know that current sensitivity is given by,

$I_s=\frac{\theta }{i}=\frac{NAB}{C}$

$I_s=\frac{80\times 50\times {10}^{-6}\times 0.2}{5\times {10}^{-9}}$

$I_s=160\times {10}^3\text{div/A}=160\text{div/mA}$

Now, voltage sensitivity is given by,

$V_s=\frac{\theta }{V}=\frac{I_s}{R}=\frac{NAB}{CR}$

$V_s=\frac{160}{20}=8\text{div/mV}$

If $V=0.01\text{mV}$,

$\theta =8\times 0.01=0.08\text{div}$

Hence, option $\left(D\right)$ is the correct answer.