Caption: Electromagnetic radiation (EMR) travels more slowly than vacuum light speed at the macroscopic scale in media.

Recall vacuum light speed c = 2.99792458*10**8 m/s (exact by definition) ≅ 3*10**8 m/s = 3*10**5 km/s ≅ 1 ft/ns.

Credit/Permission: © David Jeffery, 2003 / Own work.
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