written 5.6 years ago by
teamques10
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modified 5.1 years ago
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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 T_c, the magnetic flux is suddenly and completely expelled from it. The flux expulsion continues for T<T_c. The effect is reversible.</li>
- When the temperature is raised from below T_c. The flux density penetrates the specimen again at T=T_c and the material turns to the normal state.
- For the normal state the magnetic induction inside the specimen is given by:
$B=μ_o (H+M)=μ_o (1+χ)H$………………………………………..(1)
Here H is the applied magnetic field , m is the magnetization produced within the specimen , is χ the susceptibility of the material and $μ_o$ is the permeability of free space.
- At $T \lt T_c$ 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.