# Quantum Mechanics Expectation

1. Jun 16, 2010

### roshan2004

Quantum Mechanics "Expectation"

1. The problem statement, all variables and given/known data
1. Calculate the expectation value $$<p_{x}>$$ of the momentum of a particle trapped in a one-dimensional box.
2. Find the expectation value <x> of the position of a particle trapped in a box L wide.

2. Relevant equations
$$\psi _{n}=\sqrt{\frac{2}{L}}sin \frac{n\pi x}{L}$$
$$<p_{x}>=\int \psi^*p_{x}\psi dx$$
$$<x>=\int \psi^*x\psi dx$$

3. The attempt at a solution
I got confused on choosing the limits for both the problems for integrating them. What's the limits I should chose for both the problems.

Last edited: Jun 16, 2010
2. Jun 16, 2010

### Staff: Mentor

Re: Quantum Mechanics "Expectation"

Where is Ψ non-zero? (What are the boundaries of the box?)

3. Jun 16, 2010

### roshan2004

Re: Quantum Mechanics "Expectation"

x=0 and x=L

4. Jun 16, 2010

### roshan2004

Re: Quantum Mechanics "Expectation"

Thanks I got it. The limits that I have to use are x=0 and x=L

5. Jun 16, 2010

### Staff: Mentor

Re: Quantum Mechanics "Expectation"

Exactly.