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. | \(\dfrac{2 \mu_{0} M}{4 \pi d^{3}}\) | 2. | \(\dfrac{\mu_{0} M}{4 \pi d^{3}}\) |
3. | zero | 4. | \(\dfrac{\sqrt{5}\mu_{0} M}{4\pi d^{3}}\) |
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
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?
1.
2.
3.
4.
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'. |
For protecting a magnetic needle, it should be placed:
1. | In an iron box. |
2. | In a wooden box. |
3. | In a metallic box. |
4. | None of these. |
If the magnetic dipole moment of an atom of diamagnetic material, paramagnetic material and ferromagnetic material are denoted by \(\mu_d,~\mu_p,~\text{and}~\mu_f\) respectively, then:
1. \(\mu_p= 0 ~\text{and}~\mu_f \ne0\)
2. \(\mu_d\neq 0 ~\text{and}~\mu_p=0\)
3. \(\mu_d\ne 0 ~\text{and}~\mu_f \ne0\)
4. \(\mu_d= 0 ~\text{and}~\mu_p \ne0\)
According to Curie's law, the magnetic susceptibility of a substance at an absolute temperature T is proportional to:
1. 1/T
2. T
3. 1/T2
4. T2
Diamagnetic material in a magnetic field moves:
1. | from stronger to the weaker parts of the field |
2. | from weaker to the stronger parts of the field |
3. | perpendicular to the field |
4. | in none of the above directions |
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