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The speed of an electromagnetic wave in free space, precisely 299,792,458 m/s. Note 1: The preceding figure is precise because by international agreement the meter is now defined in terms of the speed of light. Note 2: The speed of an electromagnetic wave, e.g. , light, is equal to the product of the wavelength and the frequency. Note 3: In any physical medium, the speed of light is lower than in free space. Since the frequency is not changed, the wavelength is also decreased. [After FAA]