Q. No.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: Â Bar Magnet |
 53%
Level 3: 35%-60%
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Two permanent magnets oriented in the same direction, when brought together:
| 1. | will attract each other |
| 2. | will repel each other |
| 3. | will not exert any force on each other |
| 4. | may attract or repel each other depending on how they are brought together |
Subtopic: Â Bar Magnet |
Level 3: 35%-60%
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The magnetic field due to a short permanent magnet varies with distance \(r,\) from the magnet, as:
| 1. | \(\dfrac{1}{r}\) | 2. | \(\dfrac{1}{r^2}\) |
| 3. | \(\dfrac{1}{r^3}\) | 4. | \(\dfrac{1}{r^4}\) |
Subtopic: Â Bar Magnet |
 62%
Level 2: 60%+
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If a standard bar magnet is heated then its magnetism:
| 1. | increases | 2. | decreases |
| 3. | remains unchanged | 4. | vanishes completely |
Subtopic: Â Bar Magnet |
 67%
Level 2: 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: Â Bar Magnet |
 68%
Level 2: 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: Â Bar Magnet |
 69%
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: Â 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: Â Bar Magnet |
 79%
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: Â Bar Magnet |
 81%
Level 1: 80%+
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In which of the following situations is the interaction energy of two short bar magnets higher? The magnets are identical and held at the same separation.
| 1. | \(A\) |
| 2. | \(B\) |
| 3. | neither \(A\) nor \(B,\) since both have same energy |
| 4. | the two situations can't be compared as one is repulsive, the other attractive |
Subtopic: Â Bar Magnet |
Level 3: 35%-60%
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