Magnetism and Matter

In a uniform magnetic field of 0.049 T, a magnetic needle performs 20 complete oscillations in 5 seconds as shown. The moment of inertia of the needle is 9.8 10-6 kg m2. If the magnitude of magnetic moment of the needle is x 10-5 A m2, then the value of 'x' is : [figure]

1. 5 2
2. 128 2
3. 50 2
4. 1280 2

Match List I with List II Choose the correct answer from the options given below.

1. A-II, B-III, C-IV, D-I
2. A-II, B-I, C-III, D-IV
3. A-III, B-II, C-I, D-IV
4. A-IV, B-III, C-II, D-I

An iron bar of length L has magnetic moment M. It is bent at the middle of its length such that the two arms make an angle 60 with each other. The magnetic moment of this new magnet is :

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

The magnetic potential energy, when a magnetic bar of magnetic moment m is placed perpendicular to the magnetic field B is

1. - mB2
2. Zero
3. -mB
4. mB

The incorrect relation for a diamagnetic material (all the symbols carry their usual meaning and is a small positive number) is

1. < 0
2. 0 r < 1
3. -1 < 0
4. 1 < r < 1 +

The magnetic moment and moment of inertia of a magnetic needle as shown are, respectively, 1.0 10-2 A m2 and 10-6 2 kg m2. If it completes 10 oscillations in 10 s, the magnitude of the magnetic field is [figure]

1. 0.4 T
2. 4 T
3. 0.4 mT
4. 4 mT

The magnetic moment of an iron bar is M. It is now bent in such a way that it forms an arc section of a circle subtending an angle of 60 at the centre. The magnetic moment of this arc section is

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

The net magnetic flux through any closed surface is :

1. Positive
2. Infinity
3. Negative
4. Zero

An iron rod of susceptibility 599 is subjected to a magnetizing field of 1200 A m-1. The permeability of the material of the rod is : ( 0 = 4 10-7 T m A-1)

1. 8.0 10-5 T m A-1
2. 2.4 10-5 T m A-1
3. 2.4 10-7 T m A-1
4. 2.4 10-4 T m A-1

At a point A on the earth’s surface the angle of dip, = +25 . At a point B on the earth's surface the angle of dip, = -25 . We can interpret that :

1. A is located in the southern hemisphere and B is located in the northern hemisphere.
2. A is located in the northern hemisphere and B is located in the southern hemisphere.
3. A and B are both located in the southern hemisphere.
4. A and B are both located in the northern hemisphere.

A thin diamagnetic rod is placed vertically between the poles of an electromagnet. When the current in the electromagnet is switched on, then the diamagnetic rod is pushed up, out of the horizontal magnetic field. Hence the rod gains gravitational potential energy. The work required to do this comes from

1. The current source
2. The magnetic field
3. The lattice structure of the material of the rod
4. The induced electric field due to the changing magnetic field

If 1 and 2 be the apparent angles of dip observed in two vertical planes at right angles to each other, then the true angle of dip is given by

1. 2 = 2 1 + 2 2
2. 2 = 2 1 - 2 2
3. 2 = 2 1 - 2 2
4. 2 = 2 1 + 2 2

The magnetic susceptibility is negative for

1. ferromagnetic material only
2. paramagnetic and ferromagnetic materials
3. diamagnetic material only
4. paramagnetic material only

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

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