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Q. No.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%+
Hints
Correct relation between magnetic field \(B,\) magnetic intensity \(H,\) and intensity of magnetization \(I\) is:
1. \( B=\mu_{0}\left(H+I\right)\)
2. \(I=\mu_0\left(H+B\right)\)
3. \(H=\mu_0\left(I+B\right)\)
4. \(B=2H\left(I+\mu_0\right)\)
1. \( B=\mu_{0}\left(H+I\right)\)
2. \(I=\mu_0\left(H+B\right)\)
3. \(H=\mu_0\left(I+B\right)\)
4. \(B=2H\left(I+\mu_0\right)\)
Subtopic: Magnetization & Magnetic Intensity |
89%
Level 1: 80%+
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A short bar magnet of magnetic moment \(0.4~\text{JT}^{-1}\) is placed in a uniform magnetic field of \(0.16~\text{T}\). The magnet is in stable equilibrium when the potential energy is:
1. \(0.064~\text{J}\)
2. \(-0.064~\text{J}\)
3. zero
4. \(-0.082~\text{J}\)
1. \(0.064~\text{J}\)
2. \(-0.064~\text{J}\)
3. zero
4. \(-0.082~\text{J}\)
Subtopic: Analogy between Electrostatics & Magnetostatics |
85%
Level 1: 80%+
Please attempt this question first.
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Please attempt this question first.
Subtopic: Magnetization & Magnetic Intensity |
84%
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%+
Hints
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%
Hints
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
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%
Hints
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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