| Definition: | at a point in a medium, velocity of the envelope of a packet of superimposed sinusoidal waves of equal amplitude and slightly different frequencies tending to a common limiting frequency Note 1 to entry: The magnitude of the group velocity vector is equal to the derivative of the frequency with respect to the wavenumber. Note 2 to entry: If both group velocities and other velocities are involved, then c should be used for the former and v (vee) for the latter.
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