Before we learn why rainbows appear on CDs, we have to understand a few concepts about light. Over the years, there have been many experiments that were conducted which demonstrate these concepts. Light is everywhere in the world. It is the one thing that enables us to see. Although seeing colors and objects may seem simple to us, it actually based on a perplexing and fascinating concept of how light works. Unlike most phenomena, light can be defined as both a particle and a wave. It is a particle because it is made out of many photons which contain different amounts of energy depending on what kind of light it is. Light can also represented as a wave, like ripples in space. This particular concept is especially important when we are trying to explain how a CD works.
Light waves can exist in many different wavelengths. The reason that we see different colors is due to these different wavelengths. For example, the color green has a wavelength of 495-570 nm while red has a wavelength of 620-750 nm. This means that if a light wave has a wavelength of anywhere between 495-570nm, it will look green to us. Then what kind of wavelength does light that appears white have? Well, white light is not made up of only one kind of light wave. When all the different colors of light are combined together, it forms white light. This white light can be seen in many things such as the sun, stars, and even certain light bulbs. When white light passes through a prism, the different kinds of lights are separated by their wavelengths, resulting in what we see as a rainbow! The reason why we see different colours on a CD is because of this same concept. When light is shined on the CD, the material of the CD causes the light waves to split according to their wavelength, resulting in a rainbow!
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