A beam of white light refers to a collection of different colors of light combined together. White light is a mixture of all the visible colors of light in the electromagnetic spectrum. It is perceived as white to the human eye because it contains a balanced combination of all the visible wavelengths.
The colors in a beam of white light correspond to the different wavelengths of light within the visible spectrum. The visible spectrum ranges from approximately 400 nanometers (nm) for violet light to 700 nm for red light. In between, there are colors such as blue, green, yellow, and orange.
When white light passes through a medium, such as a prism, the different colors that make up the white light get separated due to the phenomenon of dispersion. Dispersion occurs because different colors of light have different wavelengths and hence different speeds when passing through the medium. As the light enters the prism, it refracts (bends) at different angles depending on the wavelength of each color. This bending or refraction causes the colors to spread out and become visible as a spectrum of individual colors, from violet to red.
The separation of colors in a beam of white light is due to the different indices of refraction for each color. Each color experiences a slightly different change in speed and direction as it passes through the prism. This difference causes the colors to diverge or spread apart. The phenomenon of dispersion can be observed as a rainbow-like spectrum of colors when white light passes through a prism or a raindrop, or when sunlight passes through water droplets in the atmosphere, forming a rainbow.
In this way, even though the colors are moving together through space, they get separated due to their differing wavelengths and the phenomenon of dispersion.