[Q]Expression of Group velocity in QM

1. Nov 7, 2008

good_phy

Hi.

We already know Group velocity is $\frac{\partial w }{\partial k }$

But, liboff said Group velocity is $\frac{\partial w }{\partial k }|_{k_{max}}$ where $k_{max}$ is wave number which probablity this value can be measured is higher than other wave number.

is it right? How can?

2. Nov 7, 2008

Staff: Mentor

In general, $\omega$ is a function of k, $\omega(k)$, so $d\omega / dk$ is another function of k. To get a particular velocity, you need to specify some value of k to evaluate $d\omega / dk$ at.

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