The current sensitivity of a moving coil galvanometer is $5~\text{div/mA}$ and its voltage sensitivity (angular deflection per unit voltage applied) is $20~\text{div/V}.$ The resistance of the galvanometer is: 
1. $40~\Omega$
2. $25~\Omega$
3. $250~\Omega$
4. $500~\Omega$

A $250$ turn rectangular coil of length $2.1$ cm and width $1.25$ cm carries a current of $85~\mu\text{A}$ and subjected to the magnetic field of strength $0.85~\text{T}$. Work done for rotating the coil by $180^\circ$ against the torque is:
1. $4.55~\mu\text{J}$
2. $2.3~\mu\text{J}$
3. $1.15~\mu\text{J}$
4. $9.4~\mu\text{J}$

An arrangement of three parallel straight wires placed perpendicular to the plane of paper carrying the same current in the same direction is shown in the figure. The magnitude of force per unit length on the middle wire $B$ is given by:
    
1. $\dfrac{\mu_0i^2}{2\pi d}$
2. $\dfrac{2\mu_0i^2}{\pi d}$
3. $\dfrac{\sqrt{2}\mu_0i^2}{\pi d}$
4. $\dfrac{\mu_0i^2}{\sqrt{2}\pi d}$

An electron is moving in a circular path under the influence of a transverse magnetic field of $3.57\times {10}^{-2}$ T. If the value of e/m is $1.76\times {10}^{11}$ C/kg, the frequency of revolution of the electron is

1. 1 GHz             

2. 100 MHz

3. 62.8 MHz         

4. 6.28 MHz

A square loop ABCD carrying a current i, is placed near and coplanar with a long straight conductor XY carrying a current I, the net force on the loop will be:

1. $\frac{{\mu }_{0}Ii}{2\mathrm{\pi }}$             
2. $\frac{2{\mu }_{0}IiL}{3\mathrm{\pi }}$

3. $\frac{{\mu }_{0}IiL}{2\mathrm{\pi }}$           
4. $\frac{2{\mu }_{0}Ii}{3\mathrm{\pi }}$

If a square loop ${ABCD}$ carrying a current $i$ is placed near and coplanar with a long straight conductor ${XY}$ carrying a current $I,$ what will be the net force on the loop?
                  
1. $\dfrac{\mu_0Ii}{2\pi}$
2. $\dfrac{2\mu_0IiL}{3\pi}$
3. $\dfrac{\mu_0IiL}{2\pi}$
4. $\dfrac{2\mu_0Ii}{3\pi}$