where is the magnetic permeability and is the electric permittivity. For free space, these values are 4 × 10^{-7} H/m (henries per meter) and (1/36) F/m (farads per meter), from which 120, *i.e.,* 377, ohms is obtained. In dielectric materials, the wave impedance is 377/n, where *n* is the refractive index. *Note 2:* Although the ratio is called the wave impedance, it is also the impedance of the free space or the material medium.

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