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

Concept Questions :-

Magnetization and magnetic intensity
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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. 

Concept Questions :-

Magnetic materials
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A neutral point is obtained at the centre of a vertical circular coil carrying current. The angle between the plane of the coil and the magnetic meridian is :

a) 0                           (b) 45°

(c) 60°                       (d) 90°

Concept Questions :-

Earth's magnetism
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The figure below shows the north and south poles of a permanent magnet in which n turn coil of the area of cross-section A is resting, such that for a current i passed through the coil, the plane of the coil makes an angle θ with respect to the direction of magnetic field B. If the plane of the magnetic field and the coil are horizontal and vertical respectively, the torque on the coil will be

(a)τ = niABcosθ

(b)τ = niABsinθ

(c)τ=niAB 

(d) None of the above, since the magnetic field is radial

Concept Questions :-

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Points A and B are situated perpendicular to the axis of a 2cm long bar magnet at large distances X and 3X from its centre on opposite sides. The ratio of the magnetic fields at A and B will be approximately equal to
(a) 1 : 9               (b) 2 : 9
(c) 27 : 1             (d) 9 : 1

Concept Questions :-

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Two short magnets with their axes horizontal to the magnetic meridian are placed with their centres 40 cm east and 50 cm west of the magnetic needle. If the needle remains undeflected, the ratio of their magnetic moments  is

(a) 4:5

(b) 16:25

(c) 64:125

(D) 2:5

Concept Questions :-

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If a bar magnet of magnetic moment M is freely suspended in a uniform magnetic field of strength B, the work done in rotating the magnet through an angle is

1. MB(1-sinθ)

2. MBsinθ

3. MBcosθ

4. MB(1-cosθ)

Concept Questions :-

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Two small bar magnets are placed in a line with like poles facing each other at a certain distance d apart. If the length of each magnet is negligible as compared to d, the force between them will be inversely proportional to

(a) d

(b) d2

(c) 1d2

(d) d4

 

Concept Questions :-

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A magnet of magnetic moment M is situated with its axis along the direction of a magnetic field of strength B. The work done in rotating it by an angle of 180o will be

(a) -MB                         (b) +MB

(c) 0                             (d) +2MB

Concept Questions :-

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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

Concept Questions :-

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