The speed of light is closely related to how rapidly the electric and magnetic fields in a light ray change. How rapidly the fields change is also closely related to how far apart the strong parts of the electric fields are in the wave. The speed of light is the velocity of electromagnetic waves in vacuum, which is 300,000 km/sec. Light travels slower in other media, and different wavelengths travel at different speeds in the same media. When light passes from one medium to another, it changes speed and direction, a phenomenon called refraction.

Wavelengths are associated with colors you can and cannot see.

## Determining Wavelength

When study waves, you will find that wavelength and frequency are related by an equation

Speed of the wave = Frequency x Wavelength

When you choose your radio channel, you select the Frequency. The default value is 90.0 MHz, or 90,000,000 waves per second - for an FM station. When you choose an AM station, the default frequency is 100.0 kHz, or 100,000 waves per second.

For radio waves or light waves, the Speed of the wave is the speed of light. In the United States, we often think of that as 186,000 miles per second. That's as fast as anything can go - according to Einstein's theory of relativity - which is based on Maxwell's equations for electricity and magnetism. In other countries (or when scientists use this equation), they think of the speed of light as 299,792,458 meters per second. The speed of light is the same whether we use miles per second or meters per second - only the number is different.

We use the equation to find the Wavelength - we just rearrange it so that the Wavelength is on the left

Wavelength = Speed of the wave / Frequency

Because the numbers are so big, doing this calculation by hand is a lot of work. If you were going to do it that way, you would have to solve the division problem

299,792,458 / 90,000,000

Even scientists get tired of doing that kind of problem by hand. That's why they use computers. A simple computer program to compute wavelength from frequency is demonstrated below. The instructions for this program are provided.

## A Simple Conversion Tool for Wavelength

 I listen to FM at MHz AM at kHz I want the wavelength of this radio station in Feet Meters

 Page Curator: Jay Madigan NASA Official: Dr. Lin Chambers Page Last Modified: + Freedom of Information Act + Budgets, Strategic Plans and Accountability Reports + The President's Management Agenda + Inspector General Hotline + Equal Employment Opportunity Data Posted Pursuant to the No Fear Act + Information-Dissemination Priorities and Inventories + Privacy Policy and Important Notices + USA.gov + Multimedia Browser Plug-ins + Comments or Questions?