The magnet of a vibration magnetometer is heated so as to reduce its magnetic moment by 19%. By doing this the periodic time of the magnetometer will

1. Increase by 19%       2. Decrease by 19%

3. Increase by 11%       4. Decrease by 21%

A straight wire carrying a current i is turned into a circular loop. If the magnitude of the magnetic moment associated with it in M.K.S. unit is M, the length of wire will be

1. $4\mathrm{\pi iM}$                          2. $\sqrt{\frac{4\mathrm{\pi M}}{i}}$

3. $\sqrt{\frac{4\mathrm{\pi i}}{M}}$                        4. $\frac{M\mathrm{\pi }}{4i}$

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

1. $\frac{W}{\sqrt{3}}$                    2. $\sqrt{3}W$

3. $\frac{\sqrt{3}W}{2}$                4. $\frac{2W}{\sqrt{3}}$

A magnet of magnetic moment M oscillating freely in earth's horizontal magnetic field makes n oscillations per minute. If the magnetic moment is quadrupled and the earth's field is doubled, the number of oscillations made per minute would be

1. $\frac{n}{2\sqrt{2}}$                         2. $\frac{n}{\sqrt{2}}$

3. $2\sqrt{2}n$                        4. $\sqrt{2}n$

A sensitive magnetic instrument can be shielded very effectively from outside magnetic fields by placing it inside a box of
1. Teak wood
2. Plastic material
3. Soft iron of high permeability
4. A metal of high conductivity

A uniform magnetic field, parallel to the plane of the paper existed in space initially directed from left to right. When a bar of soft iron is placed in the field parallel to it, the lines of force passing through it will be represented by:

1.		2.
3.		4.

A dip needle lies initially in the magnetic meridian when it shows an angle of dip $\theta$ at a place. The dip circle is rotated through an angle x in the horizontal plane and then it shows an angle of dip $\theta \text{'}$ . Then $\frac{\tan \theta \text{'}}{\tan \theta }$ is

1. 1/cos x

2. 1/sin x

3. 1/tan x

4. cos x

A magnetic needle is kept in a non-uniform magnetic field. It experiences

1. A force and a torque

2. A force but not a torque

3. A torque but not a force 

4. Neither a torque nor a force

The figure illustrates how B, the flux density, inside a sample of unmagnetized ferromagnetic material varies with B₀, the magnetic flux density, in which the sample is kept. For the sample to be suitable for making a permanent magnet -

1. OQ should be large and OR should be small

2. OQ and OR should both be large

3. OQ should be small and OR should be large

4. OQ and OR should both be small

A dip needle vibrates in the vertical plane perpendicular to the magnetic meridian. The time period of vibration is found to be 2 seconds. If the same needle is then allowed to vibrate in the horizontal plane and the time period is again found to be 2 seconds, then the angle of dip is:

1. 0^o

2. 30^o

3. 45^o

4. 90^o