Magnetism and Matter

A bar magnet of magnetic moment M is placed at right angles to a magnetic induction B. If a force F is experienced by each pole of the magnet, the length of the magnet will be

1. MB/F
2. BF/M
3. MF/B
4. F/MB

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

1. 2 3 J
2. 3 J
3. 3 J
4. 32 J

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

1. will become rigid showing no movement
2. will stay in any position
3. will stay in north-south direction only
4. will stay in east-west direction only

A short bar magnet of magnetic moment 0.4 J T-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

There are four light-weight-rod samples A, B, C, D separately suspended by threads. A bar magnet is slowly brought near each sample and the following observations are noted (i) A is feebly repelled (ii) B is feebly attracted (iii) C is strongly attracted (iv) D remains unaffected Which one of the following is true ?

1. B is of a paramagnetic material
2. C is of a diamagnetic material
3. D is of a ferromagnetic material
4. A is of a non-magnetic material

The magnetic moment of a diamagnetic atom is

1. much greater than one
2. 1
3. between zero and one
4. equal to zero

Electromagnets are made of soft iron because soft iron has

1. low retentivity and high coercive force
2. high retentivity and high coercive force
3. low retentivity and low coercive force
4. high retentivity and low coercive force

A vibration magnetometer placed in magnetic meridian has a small bar magnet. The magnet executes oscillations with a time period of 2 s in earth's horizontal magnetic field of 24 microtesla. When a horizontal field of 18 microtesla is produced opposite to the earth's field by placing a current carrying wire, the new time period of magnet will be

1. 1 s
2. 2 s
3. 3 s
4. 4 s

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

A bar magnet having a magnetic moment of 2 104 J T-1 is free to rotate in a horizontal plane. A horizontal magnetic field B = 6 10-4 T exists in the space. The work done in taking the magnet slowly from a direction parallel to the field to a direction 60 from the field is

1. 12 J
2. 6 J
3. 2 J
4. 0.6 J