- #1
Cogswell
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Homework Statement
Consider a particle in 1D confined in an infinite square well of width a:
$$
V(x) =
\begin{cases}
0, & \text{if } 0 \le x \le a \\
\infty, & \text{otherwise}
\end{cases}
$$
The particle has mass m and at t=0 it is prepared in the state:
$$
\Psi (x,t=0) =
\begin{cases}
A \sin (\frac{2 \pi}{a}x) \cos (\frac{\pi}{a}x), & \text{if } 0 \le x \le a \\
0, & \text{otherwise}
\end{cases}
$$
with A a real and positive number.
a. Show that ## A = \frac{2}{\sqrt{a}} ##
b. If the energy of the particle was measured, give the probability that it would be ## E = \dfrac{9 \pi^2 \hbar ^2}{2ma} ##
c. Give < ## \hat{x} ## > at t=0
d. Give < ## \hat{p} ## > as a function of time.
Homework Equations
## -\dfrac{\hbar^2}{2m} \dfrac{d^2 \psi}{dx^2} = E \psi ##
The Attempt at a Solution
I got question (a) alright, but now I'm stuck on (b).
I know that you can only get certain answers for E, because the energy levels it can be in are quantised.
In the book, it says the allowed energy levels are: ## E_n = \dfrac{n^2 \pi ^2 \hbar ^2}{2 m a ^2} ##
The one they've given me looks similar, except it's not a ## a^2 ## at the bottom. Does that mean it can never be at that energy level, and that the probability is 0?
How do you figure out the probability of a particle being at a certain energy? Is there a another probability density for that as well?