Physics
Photons: Particles of Light
Quick fact
A single photon takes about 8 minutes to travel from the Sun to Earth, but once it arrives, it can be absorbed by a single chlorophyll molecule in a plant leaf, providing the energy for photosynthesis.
Why this is interesting
You see light all around you, but have you ever wondered what it's made of? Imagine tiny packets of energy zooming through space at the speed of light — those are photons.
Read the full explanation
Understanding Photons: Particles of Light
Light behaves like a wave, but sometimes it behaves like a stream of particles. These particles are called photons. Each photon carries a specific amount of energy determined by its color or frequency. When you see light, your retina detects millions of photons. Although photons have no mass, they have momentum, which is why light can push objects like solar sails. Photons are the smallest possible unit of light — you cannot have half a photon.
A deeper explanation
Photons are quanta of the electromagnetic field. Their energy is given by E = hf, where h is Planck's constant and f is frequency. This quantization explains the photoelectric effect: electrons are ejected from a metal only when the light's frequency exceeds a threshold, regardless of intensity. Photons exhibit wave-particle duality — they travel as waves but interact as particles. They have zero rest mass, always travel at speed c in a vacuum, and carry momentum p = E/c, enabling radiation pressure. Photons mediate the electromagnetic force. Understanding photons is essential for quantum electrodynamics and technologies like lasers, where coherent photons amplify each other, and solar panels, which convert photon energy into electrical current.