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Q. No.A short magnetic dipole of a magnetic dipole moment \({M}_{0} \hat{i}\) is placed at the origin. The Magnetic field intensity at a point with a position vector \(\alpha \hat{j}+\beta\hat{k}\) is:
| 1. | \(-\dfrac{\mu_{0}{M}_{0}}{4 \pi\left(\alpha^{2}+\beta^{2}\right)^{3 / 2}}\hat{i}\) |
| 2. | \(\dfrac{\mu_{0}{M}_{0}}{2\pi\left(\alpha^{2}+\beta^{2}\right)^{3 / 2}}\hat{i}\) |
| 3. | \(\dfrac{\mu_{0}{M}_{0}}{4 \pi\left(\alpha^{2}+\beta^{2}\right)^{3 / 2}}\hat{i}\) |
| 4. | Zero |
Subtopic: Bar Magnet |
55%
Level 3: 35%-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 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 |
81%
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 |
69%
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%+
Hints
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%
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