Finding the momentum uncertainty for a particle-in-a-box

[bearsquared]

Homework Statement

I'm looking at an electron-in-a-box with walls at x=0 and x=L; I want to calculate the uncertainty (delta p) in the measurement of its momentum: sqrt(<p^2>−<p>^2) for its nth excited state.

Homework Equations

The normalized wave function: psi_n(x)=sqrt(2/L)*sin(n*pi*x/L)

The Attempt at a Solution

I'm not even sure what the p operator is for this situation. Should I just take p as -ihbar(d/dx) and sandwich p^2 and p like so? sqrt(<psi_n* | p^2 | psi_n> - <psi_n* | p | psi_n>^2)

Thanks in advance. I'll be online for a while; feel free to pop in here (http://cosketch.com/Rooms/euftgwf) if you can spare a few minutes to show me in real time.

 

[vela]

You have the right idea. Just crank it out now.