# Fermilab

## Inquiring Minds

All About Light Main Page  |  Classical  |  Relativistic  |  Quantum

 Classical - How Do We Create Electromagnetic Waves? 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

It is a fact taken from observation of nature that any object that carries charge and moves with a nonzero acceleration radiates EM waves. Of course, the properties of the radiated EM waves strongly depend on HOW the source moved, what it's acceleration was.

As a simple example, let's consider your comb, after you combed your hair. The comb is made of plastic, and it becomes charged after you brush your hair (your hair, of course, becomes charged with the equal, but opposite, charge). If one starts to wave the comb up and down, the charge on the comb moves with a nonzero acceleration, and therefore shines EM waves.

(Just for completeness, one has to add that these waves have an extremely small intensity due to small acceleration of the comb , but the fundamental idea is right. In fact, roughly, this is how a TV signal is created. No hands for combing, but alternating currents, and no charges on the combs, but free charges present in conductors.)

It should be emphasized that a charged object has to have a nonzero acceleration to be able to radiate. Steadily moving objects DO NOT radiate.

On the next page I describe the propagation of EM waves.

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