The work done in turning a magnet of magnetic moment M by an angle of 90° from the meridian, is n times the corresponding work done to turn it through an angle of 60°. The value of n is given by

2
1
0.5
0.25

Solution

A bar magnet is oscillating in the Earth’s magnetic field with a period T. What happens to its period and motion if its mass is quadrupled?

Motion remains S.H.and period remains nearly constant
Motion remains S.H. with time period = ^T⁄₂
Motion remains S.H. with time period = 2T
Motion remains S.H. with time period = 4T

Solution

Relative permittivity and permeability of a material ε_r and μ_r, respectively. Which of the following values of these quantities are allowed for a diamagnetic material?

ε_r = 0.5, μ_r= 1.5
ε_r = 1.5, μ_r= 0.5
ε_r= 0.5, μ_r= 0.5
ε_r= 1.5, μ_r= 1.5

Solution

For a diamagnetic material, the value of μ_r is less than one. For any material, the value of ε_r is always greater than 1.

Needles N₁, N₂ and N₃ are made of a ferromagnetic, aparamagnetic and a diamagnetic substance respectively. A magnet when brought close to them will

attract N₁ and N₂ strongly but repel N₃
attract N₁ strongly, N₂ weakly and repel N₃ weakly
attract N₁ strongly, but repel N₂ and N₃ weakly
attract all three of them

Solution

Ferromagnetic substance has magnetic domains where as paramagnetic substances have magnetic dipoles which get attracted to a magnetic field.Diamagnetic substances do not have magnetic dipole but in the presence of external magnetic field due to their orbital motion these substance are repelled.

If a toroid uses bismuth for its core, the field in the core compared to that in empty core will be slightly

greater
smaller
equal
None of these

Solution

Field in the core with Bismuth will be smaller because bismuth is diamagnetic.

Horizontal component of earth’s field at a height of 1m from the surface of earth is H. Its value at a height of 10 m from surface of earth is

H/10
H/9
H/100
H

Solution

The value of H is fairly uniform.

Time periods of vibation of two bar magnets in sum and difference positions are 4 sec and 6 sec respectively. The ratio of their magnetic moments M₁ / M₂ is

6 : 4
30 : 16
2. 6 : 1
1 . 5 : 1

Solution

The time period of oscillation of a magnet in a vibration magnetometer is 1.5 sec. The time period of oscillation of another magnet similar in size, shape and mass but having 1/4 magnetic moment than that of the 1st magnet oscillating at the same place will be

0.75 sec
1.5 sec
3.0 sec
6.0 sec

Solution

A steel wire of length l has a magnetic moment M. It is bent in L-shape (Figure). The new magnetic moment is

M
^M⁄_√2
^M⁄₂
2M

Solution

A thin rectangular magnet suspended freely has a period of oscillation of 4 s. If it is broken into two halves (each having half the original length) and one of the pieces is suspended similarly. The period of its oscillation will be

4 s
2 s
0.5 s
0.25 s

Solution

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