A conducting circular loop is placed in a uniform magnetic field, \(B=0.025~\text{T}\) with its plane perpendicular to the loop. The radius of the loop is made to shrink at a constant rate of \(1~\text{mm s}^{-1}\). The induced emf, when the radius is \(2~\text{cm}\), is:
1. \(2\pi ~\mu\text{V}\)
2. \(\pi ~\mu\text{V}\)
3. \(\dfrac{\pi}{2}~\mu\text{V}\)
4. \(2 ~\mu \text{V}\)

The current \((I)\) in the inductance is varying with time \((t)\) according to the plot shown in the figure. 

Which one of the following is the correct variation of voltage with time in the coil?

1.		2.
3.		4.

A coil of resistance \(400~\Omega\) is placed in a magnetic field. The magnetic flux \(\phi~\text{(Wb)}\) linked with the coil varies with time \(t~\text{(s)}\) as \(\phi=50t^{2}+4.\) The current in the coil at \(t=2~\text{s}\) is:$$
1. \(0.5~\text{A}\)
2. \(0.1~\text{A}\)
3. \(2~\text{A}\)
4. \(1~\text{A}\)

The magnetic potential energy stored in a certain inductor is \(25~\text{mJ},\) when the current in the inductor is \(60~\text{mA}.\) This inductor is of inductance:
1. \(0.138~\text H\)
2. \(138.88~\text H\)
3. \(1.389~\text H\)
4. \(13.89~\text H\)

In a coil of resistance \(10\) \(\Omega\), the induced current developed by changing magnetic flux through it is shown in the figure as a function of time. The magnitude of change in flux through the coil in Weber is:

     
1. \(2\)
2. \(6\)
3. \(4\)
4. \(8\)

The figure shows planar loops of different shapes moving out of or into a region of a magnetic field which is directed normally to the plane of the loop away from the reader. Then:

A wheel with \(10\) metallic spokes each \(0.5~\text{m}\) long is rotated with a speed of \(120~\text{rev/min}\) in a plane normal to the horizontal component of Earth’s magnetic field \(H_E\) at a place. If \(H_E=0.4~\text{G}\) at the place, what is the induced emf between the axle and the rim of the wheel? (\((1~\text{G}=10^{-4}~\text{T})\) 
1. \(5.12\times10^{-5}~\text{V}\) 
2. \(0\)
3. \(3.33\times10^{-5}~\text{V}\)
4. \(6.28\times10^{-5}~\text{V}\)

Two concentric circular coils, one of small radius \({r_1}\) and the other of large radius \({r_2},\) such that \({r_1<<r_2},\)  are placed co-axially with centres coinciding. The mutual inductance of the arrangement is:
1. \(\dfrac{\mu_0\pi r_1^2}{3r_2}\)

2. \(\dfrac{2\mu_0\pi r_1^2}{r_2}\)

3. \(\dfrac{\mu_0\pi r_1^2}{r_2}\)

4. \(\dfrac{\mu_0\pi r_1^2}{2r_2}\)

The expression for the magnetic energy stored in a solenoid in terms of magnetic field \(B\), area \(A\) and length \(l\) of the solenoid is: