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## Homework Statement

Infinite square well of length L, from -L/2 to +L/2.

Suddenly the box expands (symmetrically) to twice it's size, leaving the wave function undisturbed. Show that the probability of finding the particle in the ground state of the new box is [tex](8/3 \pi )^2[/tex].

## Homework Equations

the ground state of the wave function is

[tex] \psi = (2/L)^{(1/2)} cos(\pi x /L) [/tex]

## The Attempt at a Solution

If the wave function remains undisturbed, shouldn't the probability of finding it in the interval (-L/2, L/2) remain the same, equal to 1, and everywhere else zero? So the probability of finding it in the interval -L,L would simply be 1/2. The question is just really confusing me.