# Fermilab

## Inquiring Minds

All About Light Main Page  |  Classical  |  Relativistic  |  Quantum

 Classical - Visible Spectrum What is Light?  |  Wave's Family Members  |  Electromagnetic Waves How Do We Create Electromagnetic Waves?  |  Description of EM Waves Spectrum of Electromagnetic Waves  |  Visible Spectrum Speed of Light-First Try  |  Speed of Light in a Vacuum  |  Speed of Light in Matter
On the previous pages we learned that light is an electromagnetic wave. The visible part of the EM spectrum is very narrow, but wide enough to bring us the beautiful and colorful world all around us. What do I mean by that?

Well, the color of the light is given by its frequency. The picture below summarizes the frequencies of various colors.

An apple appears red, because an electromagnetic wave (called light) with a frequency of approximately 4x10^14 Hertz travels to your eye from the surface of the apple. The red-light-sensitive cells in your eye send a message to your brain saying: "Hello mister brain, would you please tell your body that I see a red apple, then please tell your hands to reach for it? Thank you." Similarly for objects of other colors.

This page concludes what I wanted to say from the classical point of view about the parameter FREQUENCY obtained while solving the wave equations on the" How do we create electromagnetic waves? "page.

I will discuss the important role of frequency later, when I describe light from the quantum mechanical point of view. As you will see, frequency is the parameter that defines the energy of a photon.

If you go to the next page, you will learn about the SPEED OF LIGHT!

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