# Wave speed

1. Sep 26, 2007

### pardesi

say for example there is a pulse through a string .then what exactly is wave speed or for that matter in case of unidirectional wave motion

2. Sep 26, 2007

### Staff: Mentor

Could you rephrase the question....I'm not sure what you are asking. Are you asking what determines the speed of a wave? If so, the answer is the tension and elastic modulus of the string.

3. Sep 27, 2007

### pardesi

how do u define wave speed

4. Sep 27, 2007

### ZapperZ

Staff Emeritus
What's wrong with $v=f\lambda$?

Zz.

5. Sep 27, 2007

### pardesi

i want to have the definition well the espression is well one perhaps a physical interpretation will do

6. Sep 27, 2007

### genneth

Well, you get a wave, and look at how fast the peaks and troughs are moving.

7. Sep 27, 2007

### ZapperZ

Staff Emeritus
Could you say that again and maybe, this time, include a few punctuations?

Zz.

8. Sep 27, 2007

### pardesi

Sorry i didn't realize that how difficult is it to read that line without punctuation.
Could u please define Wave speed in general mathematically

9. Sep 27, 2007

### f95toli

There is no general definition for the speed of a "wave" if you by "wave" also mean pulses etc.

*The velocity at which a plane wave would propagate through a medium $$c$$ this is a constant which depends on properties of the medium (e.g. the speed of light or the speed of sound)

*Phase velocity, $$v_p=\omega/\beta$$, is the speed at which a constant phase point (i.e. a maximum) travels. $$\beta$$ is the propagation constant.

*Group velocity $$v_g=(d\beta/dt)^{-1}$$, is the speed at which a signal (such as a pulse) propagates thorugh a medium. This is only a meaninfull concept for signals with a narrow bandwidth or in media with low dispersion.

Note that you can have $$v_p>c$$.