Physics

Problem

A solenoid of length

0.40\,\text{m}

has

800

turns and carries a steady current of

4.0\,\text{A}

. A cylindrical core of soft iron of the same length is completely inserted into the solenoid so that the field is uniform within the core. a. (i) Calculate the magnetic field

B_{0}

inside the solenoid when the core is absent. b. (ii) The relative permeability

\mu_{r}

of the iron core at room temperature is

500

. Determine the magnetic flux density

B_{\text{room}}

inside the core at room temperature. c. (iii) The core is now heated uniformly to a temperature well above its Curie temperature so that it behaves as a paramagnetic substance with

\mu_{r}=1.10

. Calculate the new magnetic flux density

B_{\text{hot}}

inside the core. d. (iv) Compare

B_{\text{room}}

and

B_{\text{hot}}

and explain, with reference to domain theory, why such a drastic change occurs on heating through the Curie temperature.

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