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Find the momentum-space wave function [itex] \Phi_n(p,t)[/itex] for the [itex]n[/itex]th stationary state of the infinite square well.

Equations:

[tex] \Psi_n(x,t) = \psi_n(x) \phi_n(t) [/tex]

[tex] \psi_n(x) = \sqrt{\frac{2}{a}}\sin(\frac{n\pi}{a}x) [/tex]

[tex] \phi_n(t) = e^{-iE_n t/\hbar} [/tex]

[tex] \Phi_n(p,t) = \frac{1}{\sqrt{2\pi\hbar}} \int^{\infty}_{-\infty} e^{-ipx/\hbar} \Psi_n(x,t) dx [/tex]

Attempt:

[tex] \Phi_n(p,t) = \frac{\phi_n(t)}{\sqrt{a\pi\hbar}} \int^{\infty}_{-\infty} e^{-ipx/\hbar} \sin(\frac{n\pi}{a}x) dx [/tex]

[tex] = \frac{\phi_n(t)}{\sqrt{a\pi\hbar}} \frac{1}{2i} \int^{\infty}_{-\infty}\Bigg(e^{i(\frac{n\pi}{a} - \frac{p}{\hbar})x} - e^{i(\frac{-p}{\hbar} - \frac{n\pi}{a})x}\Bigg) dx [/tex]

[tex] = \frac{\phi_n(t)}{\sqrt{a\pi\hbar}} \frac{1}{2i} 2\pi \Bigg(\delta(\frac{n\pi}{a} - \frac{p}{\hbar}) - \delta(\frac{p}{\hbar} + \frac{n\pi}{a})\Bigg) [/tex]

This doesn't seem right to me. Do I have this right, or am I missing something somewhere?

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# Homework Help: Infinite square well, momentum space

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