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Q. No.A sample of magnetic material is placed in a magnetic field. As the magnetic field is increased, its magnetisation increases and finally, it becomes constant — even if the field is increased further.
Now, the temperature of the sample is decreased. The magnetisation:
1.
increases
2.
decreases
3.
remains unchanged
4.
decreases first and then increases
Subtopic: Magnetic Materials |
Level 3: 35%-60%
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Assume that the magnetic field of the earth is due to a small magnetic dipole, placed at the centre of the earth (radius: \(R\)). The magnetic field at the equator is \(B_e.\) The dipole moment of the dipole is:
| 1. | \(\dfrac{\pi}{\mu_0}\left(B_eR^3\right )\) | 2. | \(\dfrac{2\pi}{\mu_0}\left(B_eR^3\right )\) |
| 3. | \(\dfrac{4\pi}{\mu_0}\left(B_eR^3\right )\) | 4. | \(\dfrac{2}{\mu_0}\left(B_eR^3\right )\) |
Subtopic: Bar Magnet |
68%
Level 2: 60%+
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Two identical magnets are placed along the \(x\text-\)axis, equidistant from the origin and opposing each other. If a third magnet be placed at the origin along the \(y\text-\)axis, with its north-pole towards the positive \(y\text-\)axis, it will experience:
| 1. | force along +ve \(y\text-\)axis |
| 2. | force along -ve \(y\text-\)axis |
| 3. | zero force but a clockwise torque |
| 4. | zero force but an anticlockwise torque |
Subtopic: Bar Magnet |
53%
Level 3: 35%-60%
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When a diamagnetic material is placed in a magnetic field, the field strength within the material is:
| 1. | increased |
| 2. | decreased |
| 3. | unchanged |
| 4. | fluctuating with time: first increasing and then decreasing |
Subtopic: Magnetic Materials |
70%
Level 2: 60%+
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Two short bar magnets are placed at large distances from each other, with their axes aligned along the same line but in opposite directions to each other. A null point is formed between them at a distance \(r_1\) from the first magnet and \(r_2\) from the second. If the dipole moments of the magnets are \(P_1\) and \(P_2\), then:
| 1. | \(\dfrac{r_1}{r_2}=\dfrac{P_1}{P_2}\) |
| 2. | \(\left(\dfrac{r_1}{r_2}\right)^2=\dfrac{P_1}{P_2} \) |
| 3. | \(\left(\dfrac{r_1}{r_2}\right)^3=\dfrac{P_1}{P_2} \) |
| 4. | none of the above is true. |
Subtopic: Bar Magnet |
71%
Level 2: 60%+
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A current carrying circular loop of wire is placed in a magnetic field \(B\), which makes an angle \(\theta\) with the normal to the loop. The radius of the loop is \(r\), and the loop carries a current \(i\). The magnetic interaction energy of the current carrying loop is \(E_B\) and the torque on the loop has the magnitude \(\tau_B\).
Which of the following, is independent of \(\theta?\)
Which of the following, is independent of \(\theta?\)
| 1. | \(E_B\cdot\tau_B\) | 2. | \(\dfrac{E_B}{\tau_B}\) |
| 3. | \(E_B^2+\tau_B^2\) | 4. | \(E_B^2-\tau_B^2\) |
Subtopic: Analogy between Electrostatics & Magnetostatics |
61%
Level 2: 60%+
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Two small paramagnetic samples are placed in an (otherwise uniform) strong external magnetic field \(B.\) If the two samples are placed with a separation that is along the direction of the external field \(B,\) then, the force exerted by the two samples on each other is:
| 1. | attractive. |
| 2. | repulsive. |
| 3. | zero. |
| 4. | any of the above depending on the external field \(B\) and the sample separation. |
Subtopic: Magnetic Materials |
56%
Level 3: 35%-60%
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A small permanent magnet is placed 'antiparallel' to a uniform magnetic field \(B.\) A null point is found at a distance \(r,\) on the axis of the magnet. Then, \(r\) is proportional to (nearly):
1. \(B^{-3}\)
2. \(B^{-2}\)
3. \(B^{-1/2}\)
4. \(B^{-1/3}\)
1. \(B^{-3}\)
2. \(B^{-2}\)
3. \(B^{-1/2}\)
4. \(B^{-1/3}\)
Subtopic: Bar Magnet |
69%
Level 2: 60%+
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A \(100\)-turn coil of wire of size \(2~\text{cm}\times 1.5~\text{cm}\) is suspended between the poles of a magnet producing a field of \(1~\text T,\) inside a galvanometer. Calculate the torque on the coil due to a current of \(0.1~\text{A}\) passing through the coil.
1. \(3 \times 10^{-5}\) N-m
2. \(30\) N-m
3. \(3 \times 10^{-3}\) N-m
4. \(3 \times 10^{-2}\) N-m
1. \(3 \times 10^{-5}\) N-m
2. \(30\) N-m
3. \(3 \times 10^{-3}\) N-m
4. \(3 \times 10^{-2}\) N-m
Subtopic: Bar Magnet |
81%
Level 1: 80%+
Hints
The coercive force for a certain magnet is \(3 \times 10^3 ~\text{A/m}\). This magnet is placed within a solenoid having \(40~\text{turns/cm}\). What current should be passed through the solenoid so that the magnet is demagnetized?
| 1. | \(0.75~\text{A}\) | 2. | \(75~\text{A}\) |
| 3. | \(1.33~\text{A}\) | 4. | \(133~\text{A}\) |
Subtopic: Magnetization & Magnetic Intensity |
69%
Level 2: 60%+
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