Question

An example of perfect diamagnetic is a superconductor. This implies that when a superconductor is put in magnetic field of intensity $B$, the magnetic field ${B_S}$ inside the superconductor will be such that:
A) ${B_S} = - B$
B) ${B_S} = 0$
C) ${B_S} = B$
D) ${B_S} < B$ but ${B_S} \ne 0$

Answer 1

Hint: Just keep in mind that a superconductor is said to be in the Meissner effect when there is no magnetic field inside it. Also. Meissner effect is originated when the current is induced in the superconductor to reject the magnetic field lines.

Complete step by step solution:
Firstly, A superconductor is a conductor that does not allow the magnetic field lines to pass through it. This effect of not allowing magnetic field lines to pass is known as Meissner’s effect. This effect happens because an induced current is set up inside the semiconductor so that on the application of an external magnetic field the superconductor faces zero resistance and the field produced by the induced current cancels the applied field.

Now, as we know, a diamagnetic substance tends to repel the magnetic field lines passing through it. Therefore, for the perfect semiconductor or superconductor, the field would not enter the superconductor. Hence, magnetic field lines inside the superconductor will be zero. Hence, we can say that the magnetic field inside the superconductor is ${B_S} = 0$ .

Hence, option (B) is the correct option.

Additional Information:
Now, we will know deeply about the Meissner effect. Meissner effect is the effect that rejects the magnetic field from the superconductor during the transition of the magnetic field to superconductor when it is cooled below its critical temperature.
Now, the Meissner effect has given a phenomenal explanation in which the electromagnetic free energy in a superconductor minimized provided that
${\Delta ^2}H = {\lambda ^{ - 2}}H$
Here, $H$ is the magnetic field and $\lambda $ is the penetration depth. This equation shows that the magnetic field in a superconductor decays exponentially. This process of exclusion of the magnetic field is the demonstration of the super demagnetisation.

Note: In the Meissner state, the total magnetic field will be very close to zero or deep around zero. When a magnetic field is applied to the superconductor, it rejects all the magnetic flux to enter it by producing the current near to its surface.