Magnetism and Matter

[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%

A straight magnetic strip has a magnetic moment of 44 Am2. If the strip is bent in a semicircular shape, its magnetic moment will be Am2. (given = 227)

Paramagnetic substances: Choose the most appropriate answer from the options given below:

1. A, B, C Only
2. A, C Only
3. A, B, C, D
4. B, D Only

The coercivity of a magnet is 5 103 A/m. The amount of current required to be passed in a solenoid of length 30 cm and the number of turns 150, so that the magnet gets demagnetised when inside the solenoid is A.

A circular coil having 200 turns, 2.5 10-4 m2 area and carrying 100 current is placed in a uniform magnetic field of 1 T. Initially the magnetic dipole moment ( M) was directed along B. Amount of work, required to rotate the coil through 90 from its initial orientation such that M becomes perpendicular to B, is J.

The magnetic moment of a bar magnet is 0.5 Am2. It is suspended in a uniform magnetic field of 8 10-2 T. The work done in rotating it from its most stable to most unstable position is:

1. 4 10-2 J
2. 16 10-2 J
3. 8 10-2 J
4. Zero

The magnetic potential due to a magnetic dipole at a point on its axis situated at a distance of 20 cm from its center is 1.5 10-5 T m. The magnetic moment of the dipole is A m2. (Given : 04 =10-7 T m A-1)