- The ratio of the permeability of a given material or medium, to the permeability of free space. It is obtained using the following formula: μr, = μ/μ0, where μr, is relative permeability, μ is the permeability of a given material or medium, and μ0 is the permeability of free space. According to this formula, the relative permeability of free space is 1. Materials whose relative permeability is less than 1 are diamagnetic, those slightly above 1 are paramagnetic, and those substantially above 1 are ferromagnetic.
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