Group velocity

Group velocity is often considered to be the wave velocity at which information travels. Often, this can be seen as the speed at which the envelope of the wave travels.

Group Velocity Media

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  Propagation of a wave packet demonstrating a phase velocity greater than the group velocity.

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  This shows a wave with the group velocity and phase velocity going in different directions. The group velocity is positive (i.e., the envelope of the wave moves rightward), while the phase velocity is negative (i.e., the peaks and troughs move leftward).

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    A wave packet.

    The envelope of the wave packet. The envelope moves at the group velocity.