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Q. No. A ferromagnetic material consists of domains in which the magnetic moments of the atoms are in the same direction within each domain. However, the domains are randomly oriented. A ferromagnetic material is placed in an external magnetic field. Then,
1.
all the domains grow in size.
2.
all the domains shrink in size.
3.
some domains grow in size, others shrink.
4.
domains rotate in the magnetic field.
Subtopic: Magnetic Materials |
Level 3: 35%-60%
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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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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 |
82%
Level 1: 80%+
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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 |
70%
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 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%+
Hints
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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The magnetic field, at a point \(10\) cm away, from a short bar magnet is \(3 \times 10^{-4}\) T, when the magnet is placed in an end-on position. If the magnet is in a broadside-on position, the field will be:
| 1. | \(6 \times 10^{-4}\) T | 2. | \(1.5 \times 10^{-4}\) T |
| 3. | \(3 \sqrt2 \times 10^{-4}\) T | 4. | \({\dfrac 3 {\sqrt 2}}\times 10^{-4}\) T |
Subtopic: Bar Magnet |
79%
Level 2: 60%+
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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:
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%
Hints
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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