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What is a photon?

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Quick answer

A photon is a single particle of light — the smallest possible packet of electromagnetic energy. Light behaves both as a wave and as a stream of these particles, and photons carry energy that depends on the light's color (frequency).

Key things to understand

  1. It's the fundamental particle of light and all electromagnetic radiation.
  2. It has no mass and always travels at the speed of light.
  3. Its energy depends on frequency — blue photons carry more than red.
  4. Light acts as both a wave and a stream of photons.
  5. Photons power vision, photosynthesis, and solar panels.

People also ask

What is a photon?
The smallest unit of light — a massless packet of electromagnetic energy that always moves at the speed of light.
Is light a wave or a particle?
Both — light shows wave-like and particle-like behavior depending on how it's measured, a cornerstone of quantum physics.
Do photons have mass?
No — photons are massless, which is why they can travel at the speed of light.