Proving the expectation value of any eigenvalue function

In summary, the person is struggling with an integration problem involving two formulas and limits of -infinity to +infinity. They are trying to find the size of the "box" the particle is in, which is from 0 to L. However, their integration is resulting in 0 instead of L/2. They are wondering if they are missing a formula.
  • #1
Cocoleia
295
4

Homework Statement


upload_2017-3-18_15-37-43.png


Homework Equations


upload_2017-3-18_15-38-16.png

upload_2017-3-18_15-40-42.png


The Attempt at a Solution


When I take the second formula, multiply by it's conjugate and then by x and do the integral of the first formula, I get 0, and not L/2, for <x>. Am I missing a formula ?
The complex conjugate of the exponential part multiplied by the exponential part simplifies to 1, and when I do the integral I end up with 0.
 
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  • #2
What are your integration limits?
 
  • #3
kuruman said:
What are your integration limits?
-infinity and +infinity, as in the first formula (the orange background)
 
  • #4
What is the size of the "box" the particle is in?
 
  • #5
kuruman said:
What is the size of the "box" the particle is in?
L? so would it be from 0 to L ?
 
  • #6
Right. The particle is confined from 0 to L.
 

1. What is the expectation value of an eigenvalue function?

The expectation value of an eigenvalue function is the average value that would be obtained if the eigenvalue function were measured multiple times. It represents the most likely outcome of a measurement on a quantum system.

2. How is the expectation value of an eigenvalue function calculated?

The expectation value of an eigenvalue function is calculated by taking the inner product of the eigenvalue function with the state vector of the quantum system. This is then multiplied by the complex conjugate of the inner product, and the result is the expectation value.

3. Can the expectation value of an eigenvalue function be negative?

Yes, the expectation value of an eigenvalue function can be negative. This can occur when the eigenvalue function has both positive and negative values, and the state vector of the quantum system has a higher probability of being in the negative region.

4. How does the expectation value of an eigenvalue function relate to the uncertainty principle?

The expectation value of an eigenvalue function is related to the uncertainty principle in that it represents the most likely outcome of a measurement. The uncertainty principle states that it is impossible to know both the exact position and momentum of a quantum system, and the expectation value helps to quantify this uncertainty.

5. Can the expectation value of an eigenvalue function change over time?

Yes, the expectation value of an eigenvalue function can change over time. This is because the state vector of a quantum system can change over time, resulting in a different inner product with the eigenvalue function and therefore a different expectation value.

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