Meissner effect proves that a superconductor exhibits perfect diamagnetism.
What is a superconductor?
A superconductor or superconductivity is discovered by Heike Kamerlingh Onnes in 1911.
Where he observed that the resistivity of mercury at approx. 4.5K (-268°C) becomes 0. And now at this point, it has achieved superconductivity.
The transition from a normal state to a superconducting state is a sudden process. The temp. at which this transition from normal to superconducting state occurs is called transition temp.
There are 2 types of superconductors known as ‘Type 1’ and ‘Type 2’ superconductors.
And after 22 years in 1933. 2 German physicists, Walther Meissner and Robert Ochsenfled discovered the “Meissner effect”.
Meissner effect (with diagrams)
The Meissner effect is the phenomenon of the superconductor, where the superconductor expels a magnetic field when it is cooled down below the critical temperature (Tc) at the transition.
When the magnetic field is applied to a material, during a normal state (at T>Tc) the material allows the magnetic field to pass through it.
But after cooling down (at T<Tc), the material behaves differently. It starts repelling the magnetic field around it.
This behavior shows that the superconductor shows the diamagnetic property.
Diamagnetism is the ability of a material to repel the magnetic field. A diamagnetic material induces a magnetic field in a direction opposite to an externally applied magnetic field.
Read More: Explanation of diamagnetism
How superconductor behaves under a magnetic field?
A material below its critical temperature acts as a superconductor. And if the magnetic field is applied to the superconductor it repels it, Meissner effect.
But, under the influence of the strong magnetic field, the superconductor restores its normal state i.e. it loses its superconductivity.
So, a magnetic field above the critical value of the magnetic field (Hc) destroys the superconductivity and restores the normal conducting state.
The critical magnetic field (Hc) depends on the temperature. A plot between the temperature and the critical magnetic field is drawn below:
Here, the lower the value of temp. , the higher the value of the critical magnetic field.
- The Meissner effect is the phenomenon where the superconductor expels the magnetic field.
- The superconductor shows perfect diamagnetism.
- The Meissner effect is discovered in 1933 by German physicists.