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MEISNER EFFECT ON SUPERCONDUCTORS

Meissner effect.

Meissner effect is the effect of temperature on a superconductor in an external magnetic field.
If an ordinary conductor (normal metal) is placed in an external magnetic field, an amount of magnetic flux passes through the conductor. Now the conductor is cooled to a very low temperature and we can find the magnetic lines passing through it. We can find magnetic flux even after the external field is switched off.
If a super conductor is placed in an external magnetic field and cooled below its critical temperature then we can observe that the magnetic lines of force are pushed out the substance.
The reason is the superconductor acts as a perfect dia magnetic substance below its critical temperature. Now if the external field is switched off (B=0), then we do not find any magnetic flux within the superconductor.
The below diagram shows the behavior of super conductor and a normal conductor at very low temperature in the external field. 
We can observe that below critical temperature the superconductor does not contain any magnetic flux when the external field is switched off whereas the normal metal contains the magnetic flux
.

As the superconductors are used in various sectors, an amount of magnetic flux must be retained with in it even after the external field is removed. Hence the shape of the superconductor is chosen as anchor ring.
When the external field is removed below the critical temperature, the lines at the outer edge of the anchor ring are thrown out the substance here as the lines near the inner edge are retained with in the substance.

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