5
MCQ (Single Correct Answer)
A paramagnetic sample shows a net magnetisation of $8 \mathrm{Am}^{-1}$ when placed in an external magnetic field of 0.6 T at a temperature of 4 K . When the same sample is placed in an external magnetic field of 0.2 T at a temperature of 16 K , the magnetisation will be
A
$\frac{32}{3} \mathrm{Am}^{-1}$
B
$\frac{2}{3} \mathrm{Am}^{-1}$
C
$6 \mathrm{Am}^{-1}$
D
$2.4 \mathrm{Am}^{-1}$
6
MCQ (Multiple Correct Answer)
$S$ is the surface of a lump of magnetic material.
A
Lines of $\mathbf{B}$ are necessarily continuous across $S$
B
Some lines of $\mathbf{B}$ must be discontinuous across $S$
C
Lines of $\mathbf{H}$ are necessarily continuous across $S$
D
Lines of $\mathbf{H}$ cannot all be continuous across $S$
7
MCQ (Multiple Correct Answer)
The primary origin (s) of magnetism lies in
A
atomic currents
B
Pauli exclusion principle
C
polar nature of molecules
D
intrinsic spin of electron
8
MCQ (Multiple Correct Answer)
A long solenoid has 1000 turns per metre and carries a current of 1 A . It has a soft iron core of $\alpha_r=1000$. The core is heated beyond the Curie temperature, $T_c$.
A
The $\mathbf{H}$ field in the solenoid is (nearly) unchanged but the $\mathbf{B}$ field decreases drastically
B
The $\mathbf{H}$ and $\mathbf{B}$ 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 $10^8$
9
MCQ (Multiple Correct Answer)
Essential difference between electrostatic shielding by a conducting shell and magnetostatic shielding is due to
A
electrostatic field lines can end on charges and conductors have free charges
B
lines of $\mathbf{B}$ can also end but conductors cannot end them
C
lines of $\mathbf{B}$ cannot end on any material and perfect shielding is not possible
D
shells of high permeability materials can be used to divert lines of $\mathbf{B}$ from the interior region