The distance between any two crests or any two troughs is the wavelength , while the height of a crest or the depth of a trough is the amplitude.
Frequency refers to the number of crests or troughs that pass a fixed point per second. The frequency of a light wave determines its color, with higher frequencies producing colors on the blue and violet end of the spectrum and lower frequencies producing colors on the red end of the spectrum.
Sound waves are not transverse waves. They are longitudinal waves , created by some type of mechanical vibration that produces a series of compressions and rarefactions in a medium.
Take a woodwind instrument, such as a clarinet. When you blow into a clarinet, a thin reed begins to vibrate. The vibrating reed first pushes against air molecules the medium , then pulls away. This results in an area where all of the air molecules are pressed together and, right beside it, an area where air molecules are spread far apart. As these compressions and rarefactions propagate from one point to another, they form a longitudinal wave, with the disturbance in the medium moving in the same direction as the wave itself.
If you study the diagram of the wave above, you'll see that longitudinal waves have the same basic characteristics as transverse waves. If the musician plays the same note while moving toward or away from a stationary listener, the note heard by the listener will indeed change -- even if the musician does nothing different.
As they were being pulled, the musicians played a single note on their horns. Ballot stationed himself beside the track and listened carefully, both as the train approached and receded. And the notes he heard were different than the notes being played by the musicians.
Although unusual, Ballot's experiment demonstrated clearly one of the most important wave phenomena known to scientists. The phenomenon is called the Doppler effect after Austrian mathematician Christian Johann Doppler, who first predicted this odd behavior of sound in Today, scientists know that the Doppler effect applies to all types of waves, including water , sound and light.
They also have a good idea why the Doppler effect occurs. And they've incorporated its principles into a variety of useful tools and gadgets.
When a star moves toward us, its wavelengths get compressed, and its spectrum becomes slightly bluer. When the star moves away from us, its spectrum looks slightly redder. To observe the so-called red shifts and blue shifts over time, planetary scientists use a high-resolution prism-like instrument known as a spectrograph that separates incoming light waves into different colors.
Researchers use the shifts in these lines as convenient markers by which to measure the size of the Doppler shift. If the star exists by itself — that is, if there is no exoplanet or companion star in its stellar system — then there will be no change in the pattern of its Doppler shifts over time. Doppler shifts are used in many fields besides astronomy.
By sending radar beams into the atmosphere and studying the changes in the wavelengths of the beams that come back, meteorologists use the Doppler effect to detect water in the atmosphere. The Doppler phenomenon is also used in healthcare with echocardiograms that send ultrasound beams through a body to measure changes in blood flow to make sure that a heart valve is working properly or to diagnose vascular diseases.
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