Photon

How it is used

Used when light behaves like a stream of particles, as in the photoelectric effect and atomic spectra. Photons are emitted or absorbed by atoms, have no mass and always travel at the speed of light in a vacuum. Blue photons carry more energy than red ones.

Example sentences

1. When the electron drops to a lower energy level, the atom emits a photon.

2. Calculate the energy of a photon of green light with a frequency of 5.6 × 10¹⁴ Hz.

Common collocations

• photon energy
• emit a photon
• absorb a photon
• stream of photons

Related terms

• quantumThe smallest separate amount of a physical quantity, such as energy, that can be absorbed or emitted. Light energy, for example, comes in quanta called photons.
• photoelectric effectThe release of electrons from a metal surface when light of high enough frequency shines on it. It showed that light energy comes in packets called photons.
• energy levelOne of the fixed amounts of energy that an electron in an atom is allowed to have. Electrons move between levels by absorbing or emitting photons.
• wave-particle dualityThe idea that light and matter can behave both as waves and as particles, depending on the experiment. Electrons, for example, can produce interference patterns.
• electromagnetic spectrumThe full range of electromagnetic waves, ordered by wavelength or frequency: radio waves, microwaves, infrared, visible light, ultraviolet, X-rays and gamma rays.

More terms: Quantum and Modern Physics

• uncertainty principle
• special relativity