| 1. | \(3 \pi \times 10^{-4}~ \text{H} /\text{m}\) | 2. | \(\pi \times 10^{-4}~ \text{H} /\text{m}\) |
| 3. | \(2 \pi \times 10^{-4} ~ \text{H} /\text{m}\) | 4. | \(4 \pi \times 10^{-4}~ \text{H} /\text{m}\) |

| 1. | (b), (c) | 2. | (b), (d) |
| 3. | (a), (c) | 4. | (a), (d) |
The coercivity of a small magnet where the ferromagnet gets demagnetized is \(3\times 10^3~\text{Am}^{-1}.\) The current required to be passed in a solenoid of length \(10~\text{cm}\) and number of turns \(100,\) so that the magnet gets demagnetized when inside the solenoid, is:
1. \(60~\text{mA}\)
2. \(3~\text{A}\)
3. \(6~\text{A}\)
4. \(30~\text{mA}\)