I'm studying EM waves right now and I don't understand phase and group velocity very well. I know the definitions of phase and group velocity from here and what they look like from http://www.csupomona.edu/~ajm/materials/animations/packets.html [Broken].(adsbygoogle = window.adsbygoogle || []).push({});

What I don't understand is why phase velocity does not carry information/energy where as group velocity does. phase velocity can exceed speed of light c because of this. To me, it doesn't make much sense what it means for phase velocity to exceed c. I look at it as k (wave number) approaching 0 so wavelength goes to infinity... But shouldn't poynting's theorem still apply for such a wave? namely a wave with phase velocity > c still carries energy. I think I'm confusing several issues here.

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# Phase, group velocity and energy

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