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What is Light?

Light is just one form of electromagnetic radiation, or electromagnetic waves. These waves are all around us and come in many sizes. The largest electromagnetic waves, with wavelengths from a few centimeters to over 100 meters are called radio waves. The smallest electromagnetic waves, with wavelengths the size of an atomic nucleus are called gamma rays. In between are microwaves, infrared light, visible light, ultraviolet light and X-rays.

Electromagnetic spectrum diagram, showing various properties at different wavelengths. Longer wavelengths have a lower frequency, and shorter wavelengths have a higher frequency.

The electromagnetic spectrum. Image credit: Wikipedia

In the 1600s both Isaac Newton and Galileo studied light. Newton used a prism to separate visible light into its various colors. Galileo attempted to measure the speed of light and concluded that its speed was too great to be measured by human reactions. 

Electromagnetic radiation and matter are the two main components of the universe. All electromagnetic radiation consists of oscillating electric and magnetic fields. These oscillations or waves, have wavelengths and frequency, just like sound waves or waves in water.

In most situations, light behaves like a wave with properties like wavelength and frequency, and is subject to diffraction and interference.

In some situations, light can be considered to behave like a particle called a photon. This particle has no mass, but carries a fixed amount of energy.