I have a wavefunction given by:(adsbygoogle = window.adsbygoogle || []).push({});

[tex]\psi = \sqrt{\frac{2}{L}}\sin \frac{n\pi x}{L}[/tex]

With boundary conditions 0<x<L.

When I compute the expectation value for the momentum like this:

[tex]\overline{p_x} = \int_0^L \sqrt{\frac{2}{L}}\sin \frac{n\pi x}{L} \left(-i\hbar \frac{\partial}{\partial x}\right)\sqrt{\frac{2}{L}}\sin \frac{n\pi x}{L} dx[/tex]

On evaluation I get:

[tex]\frac{2n\pi \hbar}{iL^2}\left[\frac{L}{2n\pi}\sin^2 \frac{n\pi x}{L}\right]_0^L = 0[/tex]

Why is the expectation value of the momentum Zero?

**Physics Forums | Science Articles, Homework Help, Discussion**

Dismiss Notice

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Expectation value of momentum of wavefunction

**Physics Forums | Science Articles, Homework Help, Discussion**