group velocity

noun

, Physics.

1. the velocity of finite numbers of waves undergoing simple harmonic motion, equal to the phase velocity when it does not vary with the wavelengths of the waves. The group velocity of the set of waves produced in water when a stone is dropped is less than the velocity of the individual waves.

Word History and Origins

Origin of group velocity¹

First recorded in 1885–90

Example Sentences

He had not distinguished correctly between group velocity and phase velocity.

From Scientific American

The "phase velocity" describes how fast waves of a given wavelength move, and the "group velocity" describes how fast the light conveys energy or information.

From Science Magazine

Only the group velocity must stay below the speed of light in a vacuum, Engheta says, and inside the wave guide, it does.

From Science Magazine

A light wave consists groups of smaller waves; the group velocity is the speed and direction of the overall wave group, the phase velocity refers to the speed and direction of a point on one of the smaller constituent waves.

From Scientific American

The electromagnetic energy of the light wave goes in the direction of the group velocity whereas the wave's effect on a particle goes in the direction of the phase velocity.

From Scientific American