What are the small particles of energy that light contains called?

The small particles of energy that light contains are called photons. Photons are fundamental particles that represent a quantum of light or other electromagnetic radiation. They carry energy and momentum, which are key to various physical phenomena, including the photoelectric effect, where light can eject electrons from materials, demonstrating the particle nature of light.

Photons are unique because they have no mass and travel at the speed of light in a vacuum. This ability to travel without a mass is crucial to understanding how light behaves in various contexts, such as in optics and quantum physics. The concept of photons helps to bridge the understanding between classical and quantum physics, as light exhibits both wave-like properties and particle-like properties depending on the situation.

In contrast, waves refer to the broader concept of how energy can propagate through space or a medium but do not specify the individual units of energy that constitute light. Electrons are negatively charged subatomic particles that are part of atoms but are not directly related to light itself in the same fundamental way. Molecules are composed of atoms and have no direct relation to the particle nature of light, being larger and more complex than photons.