A bar magnet of length l and magnetic dipole moment M is bent to form an arc which subtends an angle of 120° at centre. The new magnetic dipole moment will be

1.  3M2π

2.  33M2π

3.  3Mπ

4.  2Mπ

Subtopic:  Bar Magnet |
 57%
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A small bar magnet is placed with its north pole facing the magnetic north pole. The neutral points are located at a distance r from its centre. If the magnet is rotated by 180o, the neutral point shall be obtained at a distance of:
1. \(2r\)
2. \(\sqrt{2}r\)
3. \(2^{\frac{1}{3}}r\)
4. \(\frac{r}{2\sqrt{2}}\)

Subtopic:  Earth's Magnetism (OLD NCERT) |
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The unit of pole strength is:
1. \(\text{Am}^2\)
2. \(\text{Am}\)
3. \(\frac{\text{A}^2}{\text{m}}\)
4. \(\frac{\text{A}^2}{\text{m}^2}\)

Subtopic:  Bar Magnet |
 70%
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The magnetic field at a point \(x\) on the axis of a small bar magnet is equal to the field at a point \(y\) on the equator of the same magnet. The ratio of the distances of \(x\) and \(y\) from the centre of the magnet is:
1. \(2^{-3}\)
2. \(2^{\frac{-1}{3}}\)
3. \(2^{3}\)
4. \(2^{\frac{1}{3}}\)

Subtopic:  Bar Magnet |
 64%
From NCERT
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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

Subtopic:  Magnetization & Magnetic Intensity |
 68%
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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 :

1. 0                           2. 45°

3. 60°                       4. 90°

Subtopic:  Earth's Magnetism (OLD NCERT) |
 57%
From NCERT
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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:

1. τ=niABcosθ
2. τ=niABsinθ
3. τ=niAB
4. None of the above

 

Subtopic:  Bar Magnet |
From NCERT
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Two short magnets with their axes horizontally perpendicular 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

1. 4:5

2. 16:25

3. 64:125

4. 2:5

Subtopic:  Bar Magnet |
 63%
From NCERT
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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

1. -MB                        

2. +MB

3. 0                            

4. +2MB

Subtopic:  Bar Magnet |
 74%
From NCERT
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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

Subtopic:  Magnetic Field & Field Lines |
 72%
From NCERT
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