(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

A particle of mass m is in the ground state of the infinte square well. Suddenly the well expands to twice its original size, the right wall moving from a to 2a- leaving the wave function (momentarily) undisturbed. The energy of the particle is now measured. What will be the expectation value of energy?Hint:If you find yourself confronted with an infinite series, try ANOTHER method

2. Relevant equations

3. The attempt at a solution

The Hint is what is troubling me. I did encounter an infinite series, but I was able to find its sum using some mathematical manipulations.

But I'm curious to know what is the OTHER method the author is talking about. I thought a lot but I cant find any other method, which will not lead to an infinite series.. Any ideas?

Thanks =)

Edit: The answer I got by explicitly summing the series(which is not what the author wants me to do) is [tex]\hbar\omega[/tex], where [tex]\omega=\frac{\pi^{2}\hbar}{2ma^{2}}[/tex]. I would like to verify this as well.

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

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!

# Homework Help: Infinite square well wave function

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