A long solenoid has 1000 turns per metre and carries a current of `1A`. It has a soft iron core of `mu_r=1000`. The core is heated beyond the Curie temperature, `T_c`.

Options

A. The H field in the solenoid is (nearly) unchanged but the B field decreases drastically
B. The H and B fields in the solenoid are nearly unchanged
C. The magnetisation in the core reverses direction.
D. The magnetisation in the core diminishes by a factor of about `10^( 8)`

Explanation

To solve the problem, we need to analyze the behavior of the solenoid and its magnetic properties when the core is heated beyond the Curie temperature.

### Step-by-step Solution:

1. **Identify the Parameters**:
- The solenoid has a turn density (n) of 1000 turns/m.
- The current (I) flowing through the solenoid is 1 A.
- The relative permeability (μ_r) of the soft iron core is 1000.
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