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^( 7)`

Answer

A

Explanation

Here,for solenoid H=nI.
`rArr H=1000xx1=1000Am`
Thus, H is a constant, so it is nearly unchanged.
But `B=mu_(0)mu_(r)nI`
`= mu_(0)nImu_(r)`
=k (constant)`mu_(0)`.
Thus from above equation , we find that B varies with the variation in `mu_(r)`.
Now, for magnetisation in the core, when temperature of the iron core of solenoid is raised beyond curie temperature then it behave as paramagnetic material. where
and ` (X_(m))_("Fero")=10^(3)`
`(X_(m))_("Para")=10^(-5)`
`((X_(m))_("Fero"))/((X_(m))_("Para"))=(10^(3))/(10^(-5))=10^(6)`