# 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 $\theta$ 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:

Subtopic:  Bar Magnet |
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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:$\sqrt{5}$

Subtopic:  Bar Magnet |
63%
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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. $MB\left(1-\mathrm{sin}\theta \right)$

2. $MB\mathrm{sin}\theta$

3. $MB\mathrm{cos}\theta$

4. $MB\left(1-\mathrm{cos}\theta \right)$

Subtopic:  Analogy between Electrostatics & Magnetostatics | Bar Magnet |
77%
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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 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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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. $\frac{M}{2},\frac{m}{2}$

2. $M,\frac{m}{2}$

3. $\frac{M}{2},m$

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. $\sqrt{2}ml$

4. $\frac{1}{2}ml$

Subtopic:  Bar Magnet |
85%
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Rate of change of torque  with deflection is maximum for a magnet suspended freely in a uniform magnetic field of induction B, when

 1 $\theta ={0}^{o}$ 2 $\theta ={45}^{o}$ 3 $\theta ={60}^{o}$ 4 $\theta ={90}^{o}$

Subtopic:  Magnetic Field & Field Lines |
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Force between two identical bar magnets whose centres are r metre apart  is 4.8 N, when their axes are in the same line. If separation is increased to 2r, the force between them is reduced to

1. 2.4N                         2. 1.2N

3. 0.6N                         4. 0.3N

Subtopic:  Analogy between Electrostatics & Magnetostatics |
56%
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A bar magnet of magnetic moment 104J/T is free to rotate in a horizontal plane. The work done in rotating the magnet slowly from a direction parallel to a horizontal magnetic field of 4×10–5 T to a direction 60° from the field will be

1. 0.2 J                          2. 2.0 J

3. 4.18 J                        4. 2 × 102 J

Subtopic:  Analogy between Electrostatics & Magnetostatics | Bar Magnet |
85%
From NCERT
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