Editing Standing wave (section)

== Opposing waves ==
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File:Standing wave.gif|Standing wave in stationary medium. The red dots represent the wave [[Node (physics)|nodes]].
File:Standing wave 2.gif|A standing wave (black) depicted as the sum of two propagating waves traveling in opposite directions (red and blue).
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File:Standing wave.svg|Electric force vector (E) and magnetic force vector (H) of a standing wave.
File:Standing waves on a string.gif|Standing waves in a string&nbsp;– the [[fundamental frequency|fundamental]] mode and the first 5 [[harmonic]]s.
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File:Drum vibration mode01.gif|A [[Vibrations of a circular drum|standing wave on a circular membrane]], an example of standing waves in two dimensions.  This is the fundamental mode.
File:Drum vibration mode21.gif|A higher harmonic [[Vibrations of a circular drum|standing wave on a disk]] with two nodal lines crossing at the center.
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As an example of the second type, a ''standing wave'' in a [[transmission line]] is a wave in which the distribution of [[current (electricity)|current]], [[voltage]], or [[field strength]] is formed by the [[Superposition principle|superposition]] of two waves of the same [[frequency]] propagating in opposite directions.  The effect is a series of [[node (physics)|nodes]] (zero [[particle displacement|displacement]]) and [[anti-node]]s (maximum [[particle displacement|displacement]]) at fixed points along the transmission line.  Such a standing wave may be formed when a wave is transmitted into one end of a transmission line and is [[reflection (electrical)|reflected]] from the other end by an [[Electrical impedance|impedance]] [[Impedance matching|mismatch]], ''i.e.'', discontinuity, such as an [[wikt:open circuit|open circuit]] or a [[short circuit|short]].<ref>{{FS1037C}}</ref>  The failure of the line to transfer power at the standing wave frequency will usually result in [[attenuation distortion]].

In practice, losses in the transmission line and other components mean that a perfect reflection and a pure standing wave are never achieved.  The result is a ''partial standing wave'', which is a superposition of a standing wave and a traveling wave.  The degree to which the wave resembles either a pure standing wave or a pure traveling wave is measured by the [[standing wave ratio]] (SWR).<ref>{{citation | title=Fundamentals of Physical Acoustics | first=David T. | last=Blackstock | publisher=Wiley–IEEE | year=2000 | isbn=0-471-31979-1 |page=141}}</ref>

Another example is standing waves in the open [[ocean]] formed by waves with the same wave period moving in opposite directions. These may form near storm centres, or from reflection of a swell at the shore, and are the source of [[microbarom]]s and [[microseism]]s.