Introduction to the idea of a quantumEdit
Imagine that a beam of light is actually made up of little "packets" or "bundles" of energy, called quanta.
It's like looking at a crowd of people from above. At first, it seems as though they are one huge patch, without any spaces between them. You would never suspect that they were people. But as you move closer, you slowly begin to see that they are individuals, and when you get even closer, you may even recognize a few. Light seems like a continuous wave at first, but when we zoom in at the subatomic level, we notice that a beam of light actually consists of little "packets" of energy, or quanta. (You will not be able to tell the particles of light apart though because they are of the same energy, and thus identical. The fact that they can't be distinguished has to do with how a laser works.)
The only thing which differentiates one quantum from another is the energy contained in individual quanta (or "packets"). The "packets" are assigned a particular energy, depending on the frequency (or to put it simply: the colour) of the light wave. Quanta of Violet coloured light have the maximum energy and that of Red have the minimum energy.
This idea introduces the concept of the quantum (particle) nature of light, which is demonstrated by the photoelectric effect. When a metal surface is illuminated with light, electrons can be emitted from the surface. This is known as the photoelectric effect . It was explained by the theoretical physicist Albert Einstein.