BE Civil Engineering Semester 1 (FE First Year)University of Mumbai
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# Define the critical temperature. Slow that in the superconducting state the material is perfectly diamagnetic. - BE Civil Engineering Semester 1 (FE First Year) - Applied Physics 1

#### Question

Define the critical temperature. Slow that in the superconducting state the material is perfectly diamagnetic.

#### Solution

The critical temperature is the transition temperature at which the normal state of a conductor changes to superconducting state.
A superconducting material kept in a magnetic field expels the magnetic flux out its body when cooled below the critical temperature and exhibits perfect diamagnetism. This is called MEISSNER EFFECT.

⦁ It is found that as the temperature of the specimen is lowered to Tc, the magnetic flux is suddenly and completely expelled from it. The flux expulsion continues for T < Tc. The
effect is reversible.

⦁ When the temperature is raised from below Tc . The flux density penetrates the specimen again at T = Tc and the material turns to the normal state.
⦁ For the normal state the magnetic induction inside the specimen is given by:

B = μo (H+M) = μO(1+χ) H………………………………………..(1)

Here H is the applied magnetic field , m is the magnetization produced within the specimen , is χ the susceptibility of the material and μ is the permeability of free space.

At T<Tc as seen above

B = 0

Hence  equation (1) reduced to,

M = -H

And thus χ = M/H =-1

⦁ The specimen is therefore a perfect diamagnetic. The diamagnetism produces strong repulsion to the external magnets.
⦁ This effect is used to identify a superconductor , in levitation effect and suspension effect.

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Solution Define the critical temperature. Slow that in the superconducting state the material is perfectly diamagnetic. Concept: Meissner Effect.
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