According to Meissner Effect,a superconductor completely ejects out the magnetic flux yet we account for the penetration magnetic field into the surface of the conductor. In order to explain this,London derived two field equations by modifying Ohm’s law. London,basing on the assumption that there are two types of conduction electrons in a superconductor,namely the super-electrons and the normal electrons,put forward the idea that at any temperature the sum of the super electrons and normal electrons is equal to the conduction electron density in the material in normal state.

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