Group velocity is the speed at which the envelope of a wave packet (which can carry information or energy) travels through a medium. It represents how fast the overall shape of the wave’s amplitude — often a modulated signal — moves.
Key Points:
- It is distinct from phase velocity, which is the speed of individual wave crests.
- Mathematically, group velocity is related to the derivative of angular frequency with respect to wave number.
- In non-dispersive media, group and phase velocities are equal, but in dispersive media, they differ.
Significance:
- Determines how optical and radio signals propagate in fiber optics and waveguides.
- Critical in signal transmission, since it defines how fast a pulse or data packet arrives.
- In some exotic media, group velocity can appear to be faster than light, but this does not violate relativity because no information travels faster than light in a vacuum.