For example, a superconducting sample, which can be considered either as a perfect diamagnet or an ideally hard superconductor, easily levitates in an ambient external magnetic field.
2.
The difference from the mirror image method, which deals with a perfect type-I superconductor ( that completely expels the magnetic field, see the Meissner effect ), is that the perfectly hard superconductor screens the variation of the external magnetic field rather than the field itself.
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