- #1
broegger
- 257
- 0
I want to find the expectation value [tex]\langle x^2 \rangle[/tex] in some problem. To do this I make a change-of-variable,
and compute the expectation value [tex]\langle \xi^2 \rangle[/tex] like this:
Finally I change back to x:
I really can't see what is wrong here, but something is! I've tried it 10 times and I keep getting the wrong result.
[tex]\xi = \sqrt{\frac{m\omega}{\hslash}}x,[/tex]
and compute the expectation value [tex]\langle \xi^2 \rangle[/tex] like this:
[tex]\langle \xi^2 \rangle = \int\xi^2\vert\psi(\xi)\vert^2d\xi.[/tex]
Finally I change back to x:
[tex]\langle \xi^2 \rangle = \langle \frac{m\omega}{\hslash}x^2 \rangle = \frac{m\omega}{\hslash}\langle x^2 \rangle \Rightarrow \langle x^2 \rangle = \frac{\hslash}{m\omega}\langle \xi^2 \rangle.[/tex]
I really can't see what is wrong here, but something is! I've tried it 10 times and I keep getting the wrong result.