speed of light (c)

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 velocity of propagation of light is lower than the speed of light in free space. Since the frequency is not changed, in any physical medium, the wavelength is also decreased. [After FAA]