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The appearance of material with negative values of dielectric and magnetic permeabilities epsilon and mu and with negative index of refraction n forces to revise the accustomed forms of some well-known formulae of electrodynamics. This is connected with fact, that these correlations in repressing majority of sources is written in tacit suggestion that magnetic permeability of most of materials is mu = 1, factor of refraction n = epsilon and is undoubtedly executed the correlation n > 0. Such approach could be named as "nonmagnetic". However, if n < 0, this nonmagnetic approach can bring very hard mistakes.

Negative Refraction as a Source of Some Pedagogical Problems