Q. No.A small bar magnet is placed with its north pole facing the magnetic north pole. The neutral points are located at a distance r from its centre. If the magnet is rotated by 180o, the neutral point shall be obtained at a distance of:
1. \(2r\)
2. \(\sqrt{2}r\)
3. \(2^{\frac{1}{3}}r\)
4. \(\frac{r}{2\sqrt{2}}\)
If the angles of dip at two places are 30o and 45o respectively, then the ratio of horizontal components of earth's magnetic field at the two places will be:
(Assume net magnetic field to be equal at the two places)
1. √3 : √2
2. 1 : √2
3. 1 : √3
4. 1 : 2
A magnet is suspended in such a way that it oscillates in the horizontal plane. It makes 20 oscillations per minute at a place where dip angle is 30o and 15 oscillations per minute at a place where dip angle is 60o. The ratio of total earth's magnetic field at the two places is:
1.
2.
3. 4:9
4.
For substances hysteresis (B - H) curves are given as shown in figure. For making temporary magnet which of the following is best?
| 1. |  |
2. |  |
| 3. |  |
4. |  |
The relative permeability of a ferromagnetic substance varies with temperature (T) according to the curve:
1. A
2. B
3. C
4. D
The figure illustrates how B, the flux density, inside a sample of unmagnetized ferromagnetic material varies with B0, the magnetic flux density, in which the sample is kept. For the sample to be suitable for making a permanent magnet:
1. OQ should be large and OR should be small
2. OQ and OR should both be large
3. OQ should be small and OR should be large
4. OQ and OR should both be small
| Assertion (A): | If a compass needle is kept at the magnetic north pole of the earth, the compass needle may stay in any direction. |
| Reason (R): | The dip needle will stay vertical at the north pole of the earth. |
| 1. | Both (A) and (R) are true and (R) is the correct explanation of (A). |
| 2. | Both (A) and (R) are true but (R) is not the correct explanation of (A). |
| 3. | (A) is true but (R) is false. |
| 4. | Both (A) and (R) are false. |
Given below are two statements:
| Assertion (A): | The earth's magnetic field is due to iron present in its core. |
| Reason (R): | At a high-temperature magnet losses its magnetic property or magnetism. |
| 1. | Both (A) and (R) are true and (R) is the correct explanation of (A). |
| 2. | Both (A) and (R) are true but (R) is not the correct explanation of (A). |
| 3. | (A) is true but (R) is false. |
| 4. | Both (A) and (R) are false. |
Given below are two statements:
| Assertion (A): | At most of the points in northern hemisphere, the magnetic field is inclined to an angle below horizontal, whereas in the southern hemisphere, the magnetic field is inclined to an angle above horizontal. |
| Reason (R): | The magnetic south pole is near the geographic north pole and vice versa. |
| 1. | Both (A) and (R) are true and (R) is the correct explanation of (A). |
| 2. | Both (A) and (R) are true but (R) is not the correct explanation of (A). |
| 3. | (A) is true but (R) is false. |
| 4. | Both (A) and (R) are false. |
If \(\phi_1\) and \(\phi_2\) are the apparent angles of dip observed in two vertical planes at right angles to each other, then the true angle of dip \(\phi\) is given by:
1. \(cos^2{\phi}=cos^2{\phi_1}+cos^2{\phi_2}\)
2. \(sec^2{\phi}=sec^2{\phi_1}+sec^2{\phi_2}\)
3. \(tan^2{\phi}=tan^2{\phi_1}+tan^2{\phi_2}\)
4. \(cot^2{\phi}=cot^2{\phi_1}+cot^2{\phi_2}\)
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