Talk:Group velocity

From Wikipedia, the free encyclopedia

WikiProject Physics
Portal:Physics
 Physics Portal
This article is within the scope of WikiProject Physics, which collaborates on articles related to physics.
??? This article has not yet received a rating on the assessment scale. [FAQ]
??? This article has not yet received an importance rating within physics.

Please rate this article, and then leave comments here to explain the ratings and/or to identify the strengths and weaknesses of the article.

The group velocity of a wave is the velocity with which the overall shape of the wave's amplitude (known as the envelope of the wave) propagates through space.

I have NO idea what this means! "overall shape of ...amplitude" ? I thought amplitude was a number (scalar). Even if its a vector, tensor or other function, the claim (implicit) that it has a "shape" which propagates is unhelpful gobble-de-gook.

What about talking about wave composition? or "repeating units" (as in poly-"mers")

[edit] inconsistency with dispersion

The article here claims that:

For light, group velocity and phase velocity are related by the formula

v_g v_p = c^2 \,

where:

vp is the phase velocity
c is the speed of light in a vacuum.

but dispersion (optics) gives phase velocity:

v = \frac{c}{n}

and group velocity

v_g = c \left[ n - \lambda \frac{dn}{d\lambda} \right]^{-1}.

which imply that:

v_p v_g = c^2 \left[ n (n - \lambda \frac{dn}{d\lambda}) \right]^{-1} \not= c^2.

Something is wrong here. i don't see why \left[ n (n - \lambda \frac{dn}{d\lambda}) \right] should be equal to one. Boud 13:52, 13 September 2005 (UTC)

  • I agree, it doesn't seem right. I've removed that equation, pending a cite. --Bob Mellish 22:05, 4 October 2005 (UTC)


[edit] picture of group velocity

Leo-

Can someone please post a picture or a trailer where the group velocity is different from the phase velocity, like how the travelling wave would look in the transverse point of view?
Try http://krypton.mnsu.edu/~7364eb/Math113/groupvelocity.html unsigned
I tried to make a gif, but its a bit large. I think i need to cut out half the frames.. but i'm too lazy right now. Fresheneesz 03:34, 12 September 2006 (UTC)
Retrieved from "http://en.wikipedia.org../../../g/r/o/Talk%7EGroup_velocity_508e.html"