A photon is a particle of light, which is the basic unit of the electromagnetic field. It is also the force carrier for the electromagnetic force. The word “photon” comes from the Greek word φως (phōs), meaning “light”.
Photons are emitted whenever electrons change energy levels within atoms or molecules. They are also emitted when charged particles like electrons accelerate. photons are always in motion and have no rest mass; they travel at the speed of light in a vacuum (3 x 108 m/s).
When photons interact with matter, they can be scattered or absorbed. Scattering occurs when photons hit particles that are much larger than them, like atoms and molecules. When this happens, the photons bounce off in all directions. Absorption occurs when photons are absorbed by atoms or molecules, which causes them to increase in energy. This extra energy can be released as heat, light, or other forms of electromagnetic radiation.
The amount of scattering or absorption that takes place depends on the wavelength of the photon and the type of material it hits. For example, blue light is scattered more than red light because it has a shorter wavelength. This is why the sky looks blue: sunlight scatters off of tiny particles in Earth’s atmosphere and casts a blue hue across the sky. Similarly, green leaves appear green because they absorb red and blue light but reflect green light back to our eyes.