Signal velocity
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The signal velocity is the speed at which a wave carries information. It describes how quickly a message can be communicated (using any particular method) between two separated parties. Every signal velocity is always slower than (or equal to) the speed of a light pulse in a vacuum (by Special Relativity).
In the vast majority of cases, signal velocity is equal to group velocity (the speed of a short "pulse" or of a wave-packet's middle or "envelope"). However, in a few special cases (e.g., media designed to amplify the front-most parts of a pulse and then attenuate the back section of the pulse), group velocity can exceed even the vacuum speed of light.
Signal velocity is always[citation needed] the same as front velocity.
For light (electromagnetic waves) in vacuum, the signal velocity is the same as the group velocity and the phase velocity (the speed of any individual crest of the wave).
[edit] See also
[edit] References
- Brillouin, Léon. Wave propagation and group velocity. Academic Press Inc., New York (1960).
Velocities of Waves  |
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| Phase velocity | Group velocity | Front velocity | Velocity of energy transfer | Signal velocity | Information velocity |
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