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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The unit of pole strength is:

1. Am2

2. Am

3. A2m

4. A2m2

Subtopic:  Bar Magnet |
 69%
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A short magnetic dipole is placed at the origin with its dipole movement directed along the +x-axis. If magnetic field induction at a point P (r, 0) is \(B\hat{i}\), the magnetic field induction at point Q (0, 2r) will be:

1. \(-\frac{B}{16}\hat{i}\)

2. \(-\frac{B}{8}\hat{j}\)

3. \(\frac{B}{16}\hat{j}\)

4. \(-\frac{B}{16}\hat{j}\)

Subtopic:  Bar Magnet |
From NCERT
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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. 2-13

3. 23

4. 213

Subtopic:  Bar Magnet |
 64%
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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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)

Subtopic:  Analogy between Electrostatics & Magnetostatics | Bar Magnet |
 77%
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 |
 75%
From NCERT
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A long magnetic needle of length 2L, magnetic moment M and pole strength m units is broken into two pieces at the middle. The magnetic moment and pole strength of each piece will be:

1. M2,m2

2. M,m2

3. M2,m

4. M, m

Subtopic:  Bar Magnet |
 74%
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Two identical thin bar magnets each of length l and pole strength m are placed at the right angle to each other with the north pole of one touching south pole of the other. The magnetic moment of the system is :

1. ml

2. 2ml

3. 2ml

4. 12ml

Subtopic:  Bar Magnet |
 85%
From NCERT
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