group velocity

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Group velocity

The velocity of propagation of a group of waves forming a wave packet; also, the velocity of energy flow in a traveling wave or wave packet. The pure sine waves used to define phase velocity vp do not ever really exist, for they would require infinite extent. What do exist are groups of waves, wave packets, which are combined disturbances of a group of sine waves having a range of frequencies and wavelengths. Good approximations to pure sine waves exist, provided the extent of the media is very large in comparison with the wavelength of the sine wave. In nondispersive media, pure sine waves of different frequencies all travel at the same speed vp, and any wave packet retains its shape as it propagates. In this case, the group velocity vg is the same as vp. But if there is dispersion, the wave packet changes shape as it moves, because each different frequency which makes up the packet moves with a different phase velocity. If vp is frequency-dependent, then vg is not equal to vp. See Phase velocity, Sine wave, Wave motion

group velocity

[¦grüp və′läs·əd·ē]
(physics)
The velocity of the envelope of a group of interfering waves having slightly different frequencies and phase velocities.
References in periodicals archive ?
First, G-ER itself performs more effectively by delivering packets much faster as the group speed increases, as shown in Table 5.
028m, the wave packet remains at the front of the dipole until the end of the simulation, its group speed equal to the translational speed of the dipole.
The popular group Speed, which was disbanded last year, was also represented by the agency.
Next year Campbell plans on creating other teams with lesser and greater skill levels, including a competition team that would face other teams around the state in categories like speed jumping, group speed, double Dutch, and free style.
Pop group Speed followed up on her success before disbanding in March.
A talent agency representing popular singer Namie Amuro and the teenage group SPEED failed to declare 290 million yen in revenues for the year ended in August 1997, industry sources said Tuesday.
The sale price is a fraction of what Lloyds had been hoping to achieve, but comes as the group speeds up plans to shrink its international operations and seeks to meet regulatory demands to plug a hole in its financial reserves.
The sale price is a fraction of what Lloyds had originally hoped to achieve, but comes as the 39% state-owned group speeds up plans to shrink its international operations and seeks to meet regulatory demands to plug a hole in its financial reserves.
The sale price is a fraction of what Lloyds had originally been hoping to achieve, but comes as the 39% state-owned group speeds up plans to shrink its international operations and seeks to meet regulatory demands to plug a hole in its financial reserves.
Summary: Abu Dhabi stake comes as EBX group speeds investments; Mubadala EBX share is fund's biggest Latin America foray; Most EBX group company shares rise, led by MMX Mineracao; EBX, Mubadala consider fertilizers, LatAm expansion-Batista
Security Benefit Group Speeds Its Systems for Better Performance.
The second number at each show is an obligatory paean to the regime; the group speeds through it in two minutes.