A long solenoid has 1000 turns per metre and carries a current of 1 A. It has a soft iron core of μr = 1000. The core is heated beyond the Curie temperature, Tc .
(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 does not diminishes.
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Formula used for solenoid
H = n× l
Where H is magnetisation of the core,
n is number of turns and I is current flowing through the core.
So, H = 1000×1
= 1000Am
The value of magnetisation and relative permeability is same i.e 1000Am therefore at normal room temprature solenoid acts a ferromagnetic.
Whereas if temperature increased above cities temp it acts as paramagnetic substance.
If heated above curie temperature Thereby decrease in the suspevtibility of the core and material acts a paramagnetic
Substance .
Xm Ferro/ Xm Paramagnetic
= 10³/10^-5
=10^8
Therefore the magnetisation of the core diminishes by a factor of 10 ^8.
Hence, option a and d are correct.
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