A bar magnet having a magnetic moment of $2\times {10}^4 {\mathrm{JT}}^{-1}$ is free to rotate in a horizontal plane. A horizontal magnetic field $\mathrm{B} = 6 \times {10}^{-4} \mathrm{T}$ exists in the space. The work  done in taking the magnet slowly from a direction parallel to the field to a direction ${60}^o$ from the field is -

1.  12J

2.  6J

3.  2J

4.  0.6J

Electromagnets are made of soft iron because soft iron has

1.  high retentivity and low coercive force.

2.  low retentivity and high coercive force.

3.  high retentivity and high coercive force.

4.  low retentivity and low coercive force.

The magnet moment of a diamagnetic atom is

1.  1

2.  between zero and one

3.  equal to zero

4.  much greater than one

A short bar magnet of magnetic moment 0.4 ${\mathrm{JT}}^{-1}$ is placed in a uniform magnetic field of 0.16 T. The magnet is in stable equilibrium when the potential energy is

1.  0.064 J

2.  -0.064 J

3.  zero

4.  0.082 J

A compass needle which is allowed to move in a horizontal plane is taken to a geomagnetic pole. It

1.  will stay in north-south direction only.

2.  will stay in east-west direction only.

3.  will become rigid showing no movement.

4.  will stay in any position.

A magnetic needle suspended parallel to a magnetic field requires $\sqrt{3}$ J of work to turn it through $60°$. The torque needed to maintain the needle in this position will be

1.  $\sqrt{3}$ J 

2.  $\frac{3}{2}\mathrm{J}$

3.  $2\sqrt{3}\mathrm{J}$

4.  3J

A bar magnet of length l and magnetic dipole moment M is bent in the form of an arc as shown in the figure. The new magnetic dipole moment will be

1.  M

2.  $\frac{3}{\mathrm{\pi }}M$

3.  $\frac{2}{\mathrm{\pi }}M$

4.  $\frac{\mathrm{M}}{2}$

A proton and an alpha particle both enter a region of uniform magnetic field B, moving at right angles to the field B. If the radius of circular orbits for both the particles is equal and the kinetic energy acquired by proton is 1 MeV, the energy acquired by the alpha particle will be

1.  1 MeV

2.  4 MeV

3.  0.5 MeV

4.  1.5 MeV

The magnetic susceptibility is negative for

1.  ferromagnetic material only.

2.  paramagnetic and ferromagnetic materials.

3.  diamagnetic material only.

4.  paramagnetic material only.

If a diamagnetic substance is brought near the north or the south pole of a bar magnet, it is

1.  repelled by the north pole and attracted by the south pole.

2.  attracted by the north pole and repelled by the south pole.

3.  attracted by both the poles.

4.  repelled by both the poles.