- #1
watanake
- 4
- 0
the attachment shows my work. I honestly think maybe i did something wrong. at any rate the integrand is 1 and so not really even or odd.
any help is appreciated
Linear momentum of particle
- Thread starter watanake
- Start date
the attachment shows my work. I honestly think maybe i did something wrong. at any rate the integrand is 1 and so not really even or odd.
any help is appreciated
Answers and Replies
- #2
gabbagabbahey
Homework Helper
Gold Member
- 5,002
- 7
Where did the integral in your first step come from? Start with the definition of [itex]\langle \hat{P} \rangle[/itex]...
- #3
watanake
- 4
- 0
Sorry, I am supposed to calculate the average linear momentum.
So would be <p> =∫ψ*(x)P(hat)ψ(x)dx
P(hat) = -ih(bar)(d/dx)
So would be <p> =∫ψ*(x)P(hat)ψ(x)dx
P(hat) = -ih(bar)(d/dx)
- #4
gabbagabbahey
Homework Helper
Gold Member
- 5,002
- 7
The average linear momentum of what state?
Remember, [itex]\psi_k(x)=e^{ikx}[/itex] is just one k-mode of the full wavefunction for a free particle [itex]\psi(x)=\int_{-\infty}^{\infty} A(k) \psi_k(x)dk [/itex].
Last edited:
- #5
watanake
- 4
- 0
- #6
gabbagabbahey
Homework Helper
Gold Member
- 5,002
- 7
Does [itex]\frac{\infty}{\infty}=1[/itex]? That is essentially what you are claiming in your last step.
As for your first step, is that the definition of average momentum you are using in your course? Usually one defines the expectation value, or average, of an operator [itex]\hat{A}[/itex] in a given state [itex]|\psi\rangle[/itex] as [itex]\langle \hat{A} \rangle \equiv \langle \psi |\hat{A}|\psi \rangle[/itex].
Frankly, I'm still not 100% clear on what the original problem is. Can you post the original problem verbatim (word for word)?
- #7
pfreemind
- 5
- 0
Just evaluate the integral [;\int_{-\infty}^{\infty} dx;]. What do you get?
Also, [; <p>= m\frac{d<x>}{dt} ;], so if you can find [;<x>;], you should also be able to find [;<p>;].
Also, [; <p>= m\frac{d<x>}{dt} ;], so if you can find [;<x>;], you should also be able to find [;<p>;].