Question

when phase speed and group speed are equal？​

Answer 1

Answer:

Noting that c/n = vp, indicates that the group speed is equal to the phase speed only when the refractive index is a constant dn/dk = 0, and in this case the phase speed and group speed are independent of frequency, ω/k=dω/dk=c/n.

Answer 2

Answer:

Dispersion. When these two monochrome waves are propagating in vacuum, they have the same phase velocity c (the speed of light in vacuum), and the superposed wave's phase velocity equals its group velocity(both are c).

Explanation:

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