Q. No.A magnetic dipole experiences a torque of \(80\sqrt 3 \text{ Nm}\) when placed in uniform magnetic field in such a way that dipole moment makes angle of \(60^\circ\) with magnetic field. The potential energy of the dipole is:
1. \(-40\sqrt 3~\text{J}\)
2. \(80~\text{J}\)
3. \(-80~\text{J}\)
4. \(-60~\text{J}\)
1. \(-40\sqrt 3~\text{J}\)
2. \(80~\text{J}\)
3. \(-80~\text{J}\)
4. \(-60~\text{J}\)
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A bar magnet has total length \(2l=20 \) units and the field point \(P\) is at a distance \(d=10 \) units from the centre of the magnet. If the relative uncertainty of length measurement is \(1\%,\) then uncertainty of the magnetic field at point \(P\) is:
1. \(5\%\)
2. \(3\%\)
3. \(4\%\)
4. \(10\%\)
1. \(5\%\)
2. \(3\%\)
3. \(4\%\)
4. \(10\%\)
Subtopic: Bar Magnet |
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A straight magnetic strip has a magnetic moment of \(44~\text{Am}^2.\) If the strip is bent in a semi-circular shape, its magnetic moment will be:
(given \(\pi=\frac{22}{7}\))
1. \(28~\text{Am}^2.\)
2. \(34~\text{Am}^2.\)
3. \(46~\text{Am}^2.\)
4. \(12~\text{Am}^2.\)
(given \(\pi=\frac{22}{7}\))
1. \(28~\text{Am}^2.\)
2. \(34~\text{Am}^2.\)
3. \(46~\text{Am}^2.\)
4. \(12~\text{Am}^2.\)
Subtopic: Bar Magnet |
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A dipole having moment \(M\) is placed in two magnetic fields of strength \(B_1\) and \(B_2\) respectively. If the dipole oscillates \(60\) time in \(20\) s in \(B_1\) and \(60\) oscillations in \(30\) s in \(B_2\) . Then \(\frac{B_1}{B_2}=\)
| 1. | \(3 \over 2\) | 2. | \(2 \over 3\) |
| 3. | \(4 \over 9\) | 4. | \(9 \over 4\) |
Subtopic: Bar Magnet |
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A bar magnet having a magnetic moment of \(2.0\times10^{5}~\text{JT}^{-1}\) is placed along the direction of the uniform magnetic field of magnitude, \(B=14\times10^{-5}~\text{T}\). The work done in rotating the magnet slowly through \(60^\circ \) from the direction of the field is:
1. \(14~\text{J}\)
2. \(8.4~\text{J}\)
3. \(4~\text{J}\)
4. \(1.4~\text{J}\)
1. \(14~\text{J}\)
2. \(8.4~\text{J}\)
3. \(4~\text{J}\)
4. \(1.4~\text{J}\)
Subtopic: Bar Magnet |
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Two bar magnets oscillate in a horizontal plane in earth’s magnetic field with time periods of 3 s and 4 s respectively. If their moments of inertia are in the ratio of 3 : 2 then the ratio of their magnetic moments will be :
1. 2 : 1
2. 8 : 3
3. 1 : 3
4. 27 : 16
1. 2 : 1
2. 8 : 3
3. 1 : 3
4. 27 : 16
Subtopic: Bar Magnet |
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A conducting bar of length \({L}\) is free to slide on two parallel conducting rails as shown in the figure. Two resistors \({R}_1\) and \({R}_2\) are connected across the ends of the rails. There is a uniform magnetic field \(\vec B\) pointing into the page. An external agent pulls the bar to the left at a constant speed \({v}.\) The correct statement about the directions of induced currents \({I}_1\) and \({I}_2\) flowing through \({R}_1\) and \({R}_2\) respectively is:
| 1. | \({I}_1\) is in an anticlockwise direction and \(\text{I}_2\) is in a clockwise direction |
| 2. | Both \({I}_1\) and \({I}_2\) are in an anticlockwise direction |
| 3. | Both \({I}_1\) and \({I}_2\) are in a clockwise direction |
| 4. | \({I}_1\) is in a clockwise direction and \({I}_2\) is in an anticlockwise direction |
Subtopic: Bar Magnet |
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A small bar magnet is placed in a uniform external magnetic field of magnitude \(0.06\text{ T},\) such that its magnetic axis makes an angle of \(30^\circ\) with the field. If the magnet experiences a torque of \(0.018\text{ N-m},\) what is the minimum work required to rotate the magnet from its stable equilibrium position to its unstable equilibrium position?
1. \(7.2\times 10^{-2}~\text{J}\)
2. \(11.7\times 10^{-3}~\text{J}\)
3. \(9.2\times 10^{-3}~\text{J}\)
4. \(6.4\times 10^{-2}~\text{J}\)
Subtopic: Bar Magnet |
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A magnet of total magnetic moment \(10^{-2}\hat i~\text{A-m}^2\) is placed in a time-varying magnetic field \(B~\hat i(\cos \omega t)\) where \(B = 1~\text T\) and \(\omega = 0.125 ~\text{rad/s.}\) The work done for reversing the direction of the magnetic moment at \(t = 1\) second is:
1. \(0.01~\text J\)
2. \(0.007~\text J\)
3. \(0.028~\text J\)
4. \(0.014~\text J\)
1. \(0.01~\text J\)
2. \(0.007~\text J\)
3. \(0.028~\text J\)
4. \(0.014~\text J\)
Subtopic: Bar Magnet |
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A bar magnet is demagnetised by placing it inside a solenoid of length \(0.2~\text{m},\) having \(100\) turns, and carrying a current of \(5.2~\text{A}.\) What is the coercivity of the bar magnet?
| 1. | \(285~\text{A/m}\) | 2. | \(2600~\text{A/m}\) |
| 3. | \(520~\text{A/m}\) | 4. | \(1200~\text{A/m}\) |
Subtopic: Bar Magnet |
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