Magnetism and Matter

A bar magnet is hung by a thin cotton thread in a uniform horizontal magnetic field and is in equilibrium state. The energy required to rotate it by 60 is W. Now the torque required to keep the magnet in this new position is

1. W 3
2. 3W
3. 3W2
4. 2W 3

Following figures show the arrangement of bar magnets in different configurations. Each magnet has magnetic dipole moment m. Which configuration has highest net magnetic dipole moment ? [figure]

1. (1)
2. (2)
3. (3)
4. (4)

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

1. 2 M
2. M2
3. M
4. 3 M

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