Scientists and engineers use a number of terms to describe the different kinds of waves that they encounter. We'll be using these words in the rest of our articles about radio waves, so make sure you understand them before you read any further.
Amplitude - The vertical distance between the center of a wave and the top of the wave.
Crest - The top of a wave.
Cycle - Waves are repetitive in nature - they go up, come back down, go back up again, and so on. A cycle is one complete repetition of this motion. In the diagram below, you would complete one cycle if you walked along the wave between points A and B.
Frequency - The number of cycles that a wave goes through in a second.
Trough - The bottom of a wave.
Wavelength - The horizontal distance between the same point of a wave at two different cycles. In the diagram below, it is the straight line distance between points A and B.
There is an important relationship between the wavelength and frequency of a wave. We can describe that relationship using a simple equation:
c = λ*ƒ,
where c is the speed of light, λ (the Greek letter lambda, pronounced "lamb-duh") is the wavelength of the wave, and ƒ is its frequency. We already know the speed of light (approximately 300 million meters per second), which means that if we know either the wavelength or frequency of a wave, we can figure out the information we're missing. We can also tell how wavelength and frequency must be related to each other - if the wavelength increases, then the frequency must decrease. Similarly, if the frequency increases, then the wavelength must decrease. In the diagram below, the top wave's frequency is two times greater than the frequency of the bottom wave, and its wavelength is half as long.