Speed of Light

The speed of light in a vacuum is another Universal constant. We say that the speed of light is constant not because it is always the same, but because the speed of light in a vacuum is the same for all types of light. The speed of light actually varies (slightly) depending on the medium that it is traveling through. However, for all of our problems, we will consider the speed of light to be the speed in vacuum. This value is the same for all frequencies and is

\[c = 2.998 \times 10^8 {\rm m\;s^{-1}} \]

Note: This is really, really fast. As such in our everyday experience, light travels from place to place essentially instantaneously. Nevertheless, the speed of light is critical for our understanding as we use it to relate wavelength and frequency.