Light and Color

In this lesson, we’ll introduce the concept of waves and how this matters for understanding light.

This lesson is still under-development. Check back soon for more links and the full lesson!

todo: refer to the science of vision page, but focus on electromagnetism

You might have heard that light is “just” an electromagnetic wave. This statement is true, but on its own it simply replaces one mystery with another: what is an electromagnetic wave? For starters, a wave is some form of traveling repetitive motion in some medium. Interestingly, the wave can travel from one point to another without the need for the medium itself to travel that distance. For instance, the crests for a sea wave can be ridden all the way to the shore, but very little of the sea water actually travels along (similarly to the crest of a wave in a carpet). When our ears hear a sound, they are detecting the vibration caused by a wave traveling in the air.

Waves are characterized by their frequency (how often the repetitive motion is repeated) and speed (how fast the waves moves forward to new parts of the medium in which it travels). The speed of sound waves is hundreds of meters per second (1m≈3ft). The frequency of vibrations we can hear is between 20 to 20000 Hz (one Hertz is one vibration per second). Anything vibrating more rapidly than that is called ultra sound and we have machines that can detect it, but our ears can not. Anything under 20 Hz is also not audible, but we might be able to feel the vibrations with our fingers.

Electromagnetic waves are also waves, like sound waves, but instead of being made of traveling vibrations in matter, they are vibrations of… it is complicated. There are many metaphors we can use to describe the medium that electromagnetic waves vibrate in, and studying its inner workings has led to the greatest discoveries in Physics: general relativity and quantum mechanics. Instead of retracing the steps of physicists over two hundred years, we will give an engineer’s description of light, based what we can measure about it with the devices the physicists have created.

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