Fundamental Wave Properties
Part of the Optical Physics and Engineering book series (OPEG)
Certain properties of wave motion are manifested by water waves, such as those formed when a pebble is dropped on the surface of a still pond, as shown in Figure 1.1. Because all wave energy travels with a certain speed, such water waves move outward with a wave speed or velocity of propagation, v. Waves also have a wavelength, the distance from crest to crest; it is usually designated, as shown, by the Greek letter λ. If, in Figure 1.1, we were to position one finger so that it just touched the crests of the waves, we could feel each crest as it passes by. If the successive crests are widely separated, they touch our finger less often, less frequently, than if the crests are close together. The expression frequency is therefore used to designate how frequently (how many times in one second) the crests pass a given point. The velocity, the wavelength, and the frequency [stated as cycles per second or hertz (Hz)] are thus related by
This says simply that the shorter the wavelength the more frequently the wave crests pass a given point, and similarly, the higher the velocity, the more frequently the crests pass. No proportionality constant is needed in Equation (1.1) if the same unit of length is used for both the wavelength and the velocity and if the same unit of time (usually the second) is used for both the frequency and the velocity.
$$ f = v/\lambda $$
KeywordsSound Wave Sound Source Destructive Interference Shadow Area Knife Edge
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© Plenum Press, New York 1975