# Phase velocity

1. Jan 9, 2006

### dervast

Hi do u know what phase velocity is>? I have found it a boot for optical fibers
vp=1/(srqt(em) m denotes greek m letter

2. Jan 10, 2006

### Claude Bile

Yes that is correct, note that the equation you quote is equivalent to;

v_p = 1/(n*sqrt(e_0*m_0))

v_p = c/n

Phase velocity however is normally written as

v_g = w/k

Where w stands for the angular frequency (omega) and k is the wave-vector (or wave-number in 1D).

Phase velocity is just the velocity of the individual wave components (the velocity of the nodes, crests etc), not to be confused with group velocity which is the speed of the collective wave (or wave-packet).

Claude.

3. Jan 14, 2006

### dervast

Thx a lot.. but what do u understand if the wave velocity of one signal is larger than the wave velocity of another wave?
And what is the group velocity?
thx a lot

4. Jan 15, 2006

### dervast

Can anyone help me to this ?? If u have sometime plz reply...

5. Jan 15, 2006

### fasterthanjoao

http://en.wikipedia.org/wiki/Phase_velocity

http://en.wikipedia.org/wiki/Group_velocity

you should be able to find plenty of information in any physics textbook, or a dictionary of physics. decent libraries should have both. is there anything else you want to ask about phase velocity for your question? Claude gave a good description of what both are, please be specific with any other queries :D