Finding the probability density function given the eigenfunction

Click For Summary

Homework Help Overview

The discussion revolves around finding the probability density function associated with a given eigenfunction in quantum mechanics. The eigenfunction provided is expressed in terms of a complex exponential and a Gaussian factor.

Discussion Character

  • Exploratory, Mathematical reasoning, Assumption checking

Approaches and Questions Raised

  • Participants discuss squaring the wave function to find the probability density, noting challenges with the resulting integral. There are attempts to factorize the exponent for easier integration, and some express uncertainty about the approach due to unfamiliarity with similar problems.

Discussion Status

Some participants have made progress in understanding the wave function's properties, particularly regarding the cancellation of the imaginary part when squared. There is an ongoing exploration of the normalization constant, with one participant seeking verification of their calculations. Multiple interpretations of the integral's complexity are being considered.

Contextual Notes

Participants mention needing to integrate the probability density function to find the normalization constant, indicating a focus on ensuring the wave function is properly normalized. There is a concern about the combination of terms in the exponent affecting the integration process.

ypal
Messages
3
Reaction score
0

Homework Statement



I need to find the probability density function given the eigenfunction

Homework Equations



\psi=C\exp^({\frac{ipx}{\hbar}-\frac{x^2}{2a^2}})

The Attempt at a Solution



I tried to square the function but that gave me a nasty integral that I could not solve. I also tried to factorise the index so I could've used change of variables for the Gaussian integral. I haven't come across such a question before so I am not quite sure what to do. Please help me.
Cheers
 
Physics news on Phys.org
The probability density is given by
P(x)=|\psi(x)|^2.
Here \psi is the wave function of the particle. Calculate this square, and you'll find a pretty well-known probability distribution!
 
I've realized my mistake...face palm -_- Thanks! But I can't make progress at this point.
Edit: I need the integral to find the normalisation constant, not for the actual density function. The thing that worries me is the x^2 and x term being together at the index.
 
Last edited:
ypal said:
I need the integral to find the normalisation constant, not for the actual density function. The thing that worries me is the x^2 and x term being together at the index.
Show details of your attempt to perform the integral.
 
ypal said:

Homework Statement



I need to find the probability density function given the eigenfunction

Homework Equations



\psi=C\exp^({\frac{ipx}{\hbar}-\frac{x^2}{2a^2}})

The Attempt at a Solution



I tried to square the function but that gave me a nasty integral that I could not solve. I also tried to factorise the index so I could've used change of variables for the Gaussian integral. I haven't come across such a question before so I am not quite sure what to do. Please help me.
Cheers

Hey Guys!
I've made some progress and everything looks neat. It turns out the imaginary part vanishes when the function is squared(due to its conjugate). If someone could verify my work I'd appreciate it. Thanks!
\psi=C\exp^({\frac{ipx}{\hbar}-\frac{x^2}{2a^2}})
|\psi(x)|^2=C^2 exp^{\frac{ipx}{\hbar}-\frac{x^2}{2a^2}} . exp^{\frac{-ipx}{\hbar}-\frac{x^2}{2a^2}}
|\psi(x)|^2=C^2 exp^{-\frac{x^2}{a^2}}
Let \beta=\frac{1}{a^2}, |\psi(x)|^2=C^2 exp^{-\beta x^2}

Now I need to integrate this from -\infty to \infty and equate to 1 in order to find the normalisation constant.
C^{2}\int_{-\infty}^{\infty} exp^{-\beta x^2}=1
C^{2}\sqrt{\frac{\pi}{\beta}}=1
C^{2}=\sqrt{\frac{\beta}{\pi}}→ C=\frac{1}{\sqrt{a}\pi^{\frac{1}{4}}}

I am new to Latex...so I'm trying my best :D
 

Similar threads

  • · Replies 1 ·
Replies
1
Views
2K
  • · Replies 3 ·
Replies
3
Views
2K
  • · Replies 2 ·
Replies
2
Views
3K
Replies
8
Views
3K
Replies
8
Views
2K
  • · Replies 9 ·
Replies
9
Views
2K
  • · Replies 1 ·
Replies
1
Views
1K
Replies
4
Views
3K
  • · Replies 6 ·
Replies
6
Views
3K
  • · Replies 14 ·
Replies
14
Views
3K