What is a photon?

A photon is a fundamental particle of light and all other forms of electromagnetic radiation. It is the quantum or discrete unit of electromagnetic energy. Photons are unique in several ways:

Key Characteristics of a Photon:

1. Energy: Photons carry energy, which is directly proportional to the frequency of the radiation. The higher the frequency, the more energy a photon has. The energy $EE$ of a photon is given by the equation:

   $E=h\cdot f$where:

   • $EE$ is the energy of the photon,
   • $hh$ is Planck’s constant ($6.626\times 10^{-34}6.626\; \backslash times\; 10^\{-34\}$Joule-seconds),
   • $ff$ is the frequency of the radiation.
2. Massless: Photons have no rest mass, meaning they do not have mass when at rest. They always travel at the speed of light in a vacuum ($c=3\times 10^{8}c\; =\; 3\; \backslash times\; 10^8$meters per second).
3. Wave-Particle Duality: Photons exhibit both particle-like and wave-like properties, a concept known as wave-particle duality. As waves, photons exhibit characteristics such as interference and diffraction; as particles, they can be thought of as discrete packets of energy.
4. Speed: Photons always travel at the speed of light in a vacuum, regardless of their energy or frequency.
5. No Electric Charge: Photons have no electric charge, meaning they do not interact with electric fields in the same way charged particles do.
6. Interaction with Matter: Photons can interact with matter, for example, when they are absorbed or emitted by atoms during processes such as photoelectric effect (where electrons are ejected from a material when exposed to light) or stimulated emission (which forms the basis for lasers).

Examples of Photon Sources:

• Sunlight: The Sun emits photons, which are responsible for the visible light we see.
• Radio waves, X-rays, and Gamma rays: These are also forms of electromagnetic radiation, but with different photon energies and wavelengths.

Photons are the basic units of light and electromagnetic radiation, exhibiting both particle and wave properties, and they play a crucial role in a wide range of physical phenomena.