Magnetism and Matter

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

Curie temperature above which

1. paramagnetic material becomes ferromagnetic material
2. ferromagnetic material becomes diamagnetic material
3. ferromagnetic material becomes paramagnetic material
4. paramagnetic material becomes diamagnetic material

Nickel shows ferromagnetic property at room temperature. If the temperature is increased beyond Curie temperature, then it will show

1. anti ferromagnetism
2. no magnetic property
3. diamagnetism
4. paramagnetism

Curie temperature is the temperature above which

1. paramagnetic material becomes ferromagnetic material
2. ferromagnetic material becomes diamagnetic material
3. ferromagnetic material becomes paramagnetic material
4. paramagnetic material becomes diamagnetic material

If the magnetic dipole moment of an atom of diamagnetic material, paramagnetic material and ferromagnetic material are denoted by d, p and f respectively, then

1. d = 0 and p 0
2. d 0 and p = 0
3. p = 0 and f 0
4. d 0 and f 0

A diamagnetic material in a magnetic field moves

1. from stronger to the weaker parts of the field
2. from weaker to the stronger parts of the field
3. perpendicular to the field
4. in none of the above directions

According to Curie's law, the magnetic susceptibility of a substance at an absolute temperature T is proportional to

1. 1/T
2. T
3. 1/T2
4. T2