Photon Definition: A photon is a discrete packet of energy associated with electromagnetic radiation (light). A photon has energy E which is proportional to the frequency ν of the radiation: E = hν, where h is Planck's constant.
Also Known As: quantum, quanta (plural)
Characteristics
Photons are unique in that they have characteristics of both particles and waves at the same time. For students, it remains unclear as to whether a photon is a particle that travels in a wave pattern or a wave broken up into particles. Most scientists simply accept the photon as a unique packet of energy that has characteristics of both waves and particles.
Properties of a Photon
- Behaves like a particle and a wave, simultaneously
- Moves at a constant velocity, c = 2.9979 x 108 m/s (i.e. "the speed of light"), in empty space
- Has zero mass and rest energy
- Carries energy and momentum, which are also related to the frequency (nu) and wavelength (lamdba) of the electromagnetic wave, as expressed by the equation E = h nu and p = h / lambda.
- Can be destroyed/created when radiation is absorbed/emitted.
- Can have particle-like interactions (i.e. collisions) with electrons and other particles, such as in the Compton effect in which particles of light collide with atoms, causing the release of electrons.