Question

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

• A. The $\overline { \mathrm { H } }$ field in the solenoid is (nearly) unchanged but $\overline { \mathrm { B } }$ field decreases drastically.
• B. The $\overline { \mathrm { H } }$ and $\overline { \mathrm { B } }$ fields in the solenoid are nearly unchanged.
• C. The magnetisation in the core reverses direction.
• D. The $\overline { \mathrm { H } }$ field in the solenoid decreases but $\overline { \mathrm { B } }$ field increases drastically.

Answer 1

Answer: (A)

The $\overline { \mathrm { H } }$ field in the solenoid is (nearly) unchanged but $\overline { \mathrm { B } }$ field decreases drastically.

Answer 2

: In solenoid, $\overline { \mathrm { H } }$ field,

H = nI and B field

B =

Now the core is heated beyond the curie temperature

due to that decrease and hence B will also decrease.