The coercive force for a certain prmanent magnet is `4.0 xx 10^4 A m^(-1)`. This magnet is placed inside a long solenoid of 40 turns/cm and a current is passed in the solenoid to demagnetize it completely. Find the current.

Explanation

To solve the problem, we need to find the current required to demagnetize a permanent magnet placed inside a solenoid. We are given the coercive force (H) and the number of turns per unit length (n) of the solenoid.

### Step-by-Step Solution:

1. **Identify Given Values:**
- Coercive force, \( H = 4.0 \times 10^4 \, \text{A/m} \)
- Number of turns per unit length, \( n = 40 \, \text{turns/cm} \)

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