Photon

A photon is a particle that carries electromagnetic radiation. It is the fundamental unit of light.

  • A photon is an elementary particle, a quantum of light , so a photon is the smallest quantity (quantum, plural quanta) into which light can be divided.
  • Light can exhibit both wave-like and particle-like behaviour. So at times light behaves as a wave, at others, it behaves like both waves and photons, and at others just as particles.
  • Photons are the force carriers of radiant energy (electromagnetic radiation).
  • Photons can be emitted or absorbed by charged particles such as electrons and protons.
  • Photons carry energy and momentum, which are proportional to their frequency and wavelength respectively.
  • Photons can interact with matter through processes such as scattering, absorption, and emission.
  • Photons can be polarized, meaning their electric and magnetic fields oscillate in a particular direction.
  • Photons do not have mass and propagate at the speed of light in a vacuum. We can break this statement down as follows:
    • According to the theory of relativity, any object that has mass requires energy to accelerate.
    • The amount of energy required to accelerate an object increases as the object’s mass increases.
    • Photons are unique in that they have zero rest mass, which means they do not require any energy to be accelerated.
    • As a result, they always move at the speed of light in a vacuum.
    • So photons always travel at the speed of light and never slow down or come to a stop.
  • The fact that photons have zero rest mass has important implications for the behaviour of light and electromagnetic radiation in general. It means that:
    • The energy of a photon is directly proportional to its frequency (as described by Planck’s law).
    • The momentum of a photon is proportional to its frequency and direction of travel (as described by Einstein’s theory of relativity).
About the properties of photons
  • A photon is a type of elementary particle that is a quantum (plural = quanta) of the electromagnetic field. This means that it is the smallest quantity into which light can be divided.
  • A photon carries energy and can be described both in terms of a particle and a wave.
  • While the wave model of light works well for some phenomena, the particle model is necessary to explain others.
  • Light can exhibit both wave-like and particle-like behaviour depending on the experiment performed. This is known as wave-particle duality.
  • The wavelength of a photon determines its energy and frequency.
  • Photons with longer wavelengths have lower energy and frequency, while photons with shorter wavelengths have higher energy and frequency.
  • The wavelength of a photon can also affect its behaviour, such as its ability to penetrate materials or cause photochemical reactions.

Other properties of photons include:

  • Photons have zero rest mass but have energy and momentum proportional to their frequency.
  • Unlike other kinds of elementary particles, photons have no rest mass.
  • Photons are electrically neutral, meaning they have no electric charge.
  • Photons are stable particles that do not decay over time.
  • Photons can interact with other particles, such as electrons, through processes such as absorption and emission.
  • Photons can interact with other particles, such as electrons, through processes like absorption and emission.
  • Photons always travel at the speed of light in a vacuum, regardless of their frequency or energy.