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Nov20-12, 05:19 PM
jtbell's Avatar
P: 11,781
Quote Quote by mycotheology View Post
According to the wiki page, this diagram:

shows the phase velocity and group velocity moving in opposite directions. I think I understand what group velocity is, its the velocity of the overall wavepacket, in the diagram I can see a Gaussian wavepacket moving to the right so I'm guessing thats the group velocity.

I can't see the phase velocity.
The phase velocity refers to the individual waves "inside" the wave packet, which are moving to the left in your example. Actually, what you're seeing is the average phase velocity of the individual waves that combine to produce the wave packet.