Q. No.The vertical component of Earth’s magnetic field at a place is equal to the horizontal component. What is the value of the angle of dip at this place?
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At a certain location in Africa, a compass points 12° west of the geographic north. The north tip of the magnetic needle of a dip circle placed in the plane of magnetic meridian points 60° above the horizontal. The horizontal component of the earth’s field is measured to be 0.16 G. The magnitude of the earth’s field at the location is:
1. 0.16 G
2. 0.48 G
3. 0.32 G
4. 0.30 G
Figure shows two small identical magnetic dipoles \(a\) and \(b\) of magnetic moments \(M\) each, placed at a separation \(2d\), with their axes perpendicular to each other. The magnetic field at the point \(P\) midway between the dipoles is:
1. \(\frac{2 \mu_{0} M}{4 \pi d^{3}}\)
2. \(\frac{\mu_{0} M}{4 \pi d^{3}}\)
3. zero
4. \(\frac{\sqrt{5}\mu_{0} M}{4\pi d^{3}}\)
A magnetic needle suspended by a silk thread is vibrating in the earth's magnetic field. If the temperature of the needle is increased, then:
| 1. | the time period decreases. |
| 2. | the time period remains unchanged. |
| 3. | the time period increases. |
| 4. | the time period first decreases then increases. |
A ferromagnetic substance is placed in the varying magnetising field H. The magnetic induction B is a measure for various values of the direct and reverse magnetising field. The following graph has been plotted for B versus H. Choose the wrong statement:
| 1. | There is a limit of direct and reverse external magnetising field at which the magnetisation and hence the magnetic induction saturates. |
| 2. | Even after removing the external magnetising field, some residual magnetisation called 'retentivity' is left over the substance. |
| 3. | On increasing the reverse magnetising field, the magnetic induction decreases to zero for a value of the magnetising field which is known as 'susceptibility'. |
| 4. | On increasing the reverse magnetising field, the magnetic induction decreases to zero for a value of magnetising field known as 'coercivity'. |
The material suitable for making electromagnets should have:
1. High retentivity and high coercivity
2. High retentivity and low coercivity
3. Low retentivity and high coercivity
4. Low retentivity and low coercivity
Choose the correct statement regarding magnetism.
| 1. | Paramagnetic sample displays greater magnetization when cooled. |
| 2. | Diamagnetism is almost independent of temperature. |
| 3. | Ferromagnetic substances show hysteresis. |
| 4. | All of these. |
A long solenoid has 1500 turns per metre and an iron core of = 1100 is kept inside it. 2A current flows in the coil of the solenoid. If the core is heated beyond curie temperature, then:
| 1. | The H and B fields in the solenoid reduce to zero. |
| 2. | The H and B fields in the solenoid remain unchanged. |
| 3. | The H field in the solenoid is nearly unchanged but B field decreases significantly. |
| 4. | The B field in the solenoid is nearly unchanged but the H field decreases significantly. |
As we go from the magnetic equator towards the geographic south pole, the angle of the dip will become:
| 1. | More and more vertically downward and perpendicular to the surface at the magnetic pole. |
| 2. | More and more vertically upward and perpendicular to the surface at the magnetic pole. |
| 3. | Less and less vertically downward and horizontal at the magnetic pole. |
| 4. | Less and less vertically upward and horizontal at the magnetic pole. |
A material when heated suddenly changes its magnetic property at a particular temperature and above this temperature, its susceptibility is found to be inversely proportional to the absolute temperature. The material may be:
1. Ferromagnetic
2. Diamagnetic
3. Paramagnetic
4. Ferromagnetic or Paramagnetic
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