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move one's hand to and from in greeting or as a signal.

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A wavelength is the distance between the crests of waves. Licensed from iStockPhoto. Wavelength is the distance between the crests of waves or a person's general attitude. An example of wavelength is the distance between the crest of two waves.

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Physics One half the full extent of a vibration, oscillation, or wave. The amplitude of an ocean wave is the maximum height of the wave crest above the level of calm water, or the maximum depth of the wave trough below the level of calm water. The Amplitude of a pendulum swinging through an angle of 90° is 45°.

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frequency definition. In physics, the number of crests of a wave that move past a given point in a given unit of time. The most common unit of frequency is the hertz (Hz), corresponding to one crest per second.

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Wave speed is the speed at which a wave travels.Wave speed is related to wavelength, frequency, and period by the equation wave speed = frequency x wavelength. The most commonly used wave speed is the speed of visible light, an electromagnetic wave.

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a wave of compression and rarefaction, by which sound is propagated in an elastic medium such as air.

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Generally, electromagnetic radiation is classified by wavelength into radio wave, microwave, terahertz (or sub-millimeter) radiation, infrared, the visible region that is perceived as light, ultraviolet, X-rays and gamma rays. The behavior of EM radiation depends on its wavelength.