A photon is a particle of light and is the basic unit that makes up all electromagnetic radiation. photons are emitted when an atom or molecule undergoes a change in energy level, and are absorbed when they are incident on another atom or molecule and raise its energy level. The word “photon” comes from the Greek word for light, phos.
When a photon is emitted from an atom, it carries away with it some of the atom’s energy. The amount of energy carried by a photon depends on its frequency: higher-frequency photons carry more energy than lower-frequency ones. The frequency of a photon also determines its color: red photons have lower frequencies than blue photons, for example.
The speed of light in a vacuum is always the same, regardless of the wavelength (or color) of the light; however, in materials such as glass or water, different colors travel at different speeds (this effect is called dispersion). This means that when white light shines through a prism (made of glass), it bends and splits into its component colors: red, orange, yellow, green, blue, indigo, and violet.
