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THE ENERGY OF WAVES
v = (lambda)(nu) (a wave's velocity = its wavelength * its frequency) p = h/(lambda) (a wave's momentum = Planck's constant / its wavelength) Waves are one way to move energy from one place to another without having to move any matter along with it. Instead, the matter moves back and forth, or up and down, or side to side, and the energy "travels" from one piece of matter to another, along a chain of "waving matter" as it moves. When we speak of the speed or velocity of a wave, we're talking about the speed that the energy moves, not the speed at which the matter moves. We've all seen waves on a lake or pond, or even in a bathtub. The distance from one crest to the next is called the wavelength, and the number of waves that pass any specific location over a period of time is called the frequency. Wavelength is measured with any unit of length (e.g. meter), while frequency is typically measured with the unit "per second," as in "10 wave crests pass this point per second." Since "per second" is a little awkward to say, we sometimes call the unit of frequency "cycles per second" in conversation. It turns out that, because of quantum mechanics, all particles in the universe travel in waves. The wavelengths are microscopically tiny, however, so we don't see these waves unless we're studying the atomic realm. This is the basis of the second equation above, which was first derived by Louis de Broglie to describe the wavelike properties of any particle (massive or massless). Remember that the momentum of any particle is its mass times its velocity. For reference, h = 6.63 * 10^-34 Joule sec. The speed of a light wave is c = 3 * 10^8 m/sec. |