Magnetism and Matter

A short bar magnet placed with its axis at 30 with an external field of 800 Gauss, experiences a torque of 0.016 N m. The work done in moving it from most stable to most unstable position is 10-3 J. The value of is .

Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R). Consider a ferromagnetic material : In the light of the above statements, choose the correct answer from the options given below :

1. (A) is true but (R) is false
2. Both (A) and (R) are true and (R) is the correct explanation of (A)
3. (A) is false but (R) is true
4. Both (A) and (R) are true but (R) is not the correct explanation of (A)

The percentage increase in magnetic field (B) when space within a current carrying solenoid is filled with magnesium (magnetic susceptibility Mg = 1.2 10-5) is :

1. 53 10-5\%
2. 56 10-4\%
3. 56 10-5\%
4. 65 10-3\%

Given below are two statements : one is labelled as Assertion (A) and the other is labelled as Reason (R). In the light of the above statements, choose the most appropriate answer from the options given below:

1. Both (A) and (R) are correct and (R) is the correct explanation of (A)
2. (A) is not correct but (R) is correct
3. (A) is correct but (R) is not correct
4. Both (A) and (R) are correct but (R) is not the correct explanation of (A)

A magnetic dipole experiences a torque of 80 3 N m when placed in uniform magnetic field in such a way that dipole moment makes angle of 60 with magnetic field. The potential energy of the dipole is:

1. -40 3 J
2. -80 J
3. 80 J
4. -60 J

The relationship between the magnetic susceptibility ( ) and the magnetic permeability ( ) is given by : ( 0 is the permeability of free space and r is relative permeability)

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

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

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

[figure] A bar magnet has total length 2l = 20 units and the field point P is at a distance d = 10 units from the centre of the magnet. If the relative uncertainty of length measurement is 1\%, then uncertainty of the magnetic field at point P is :

1. 10%
2. 5%
3. 3%
4. 4%