Quantum Mechanics: Particle in a Box Periodic BC's

In summary, the conversation discusses solving the Schrodinger equation for a particle in a box with periodic conditions and finding the values of A and B. The normalization condition and periodicity allow for solving for A and k, and the solution can be written in the form of ##\psi(x) = A \cos(kx+\phi)##.
  • #1
Xyius
508
4

Homework Statement


The question says to solve the Schrodinger equation for a particle in a box with periodic conditions and then it gives.
ψ(0)=ψ(a)

The Attempt at a Solution


I used the above BC and I also did it as its derivative. (It wasn't stated but I assumed it was implied. I had no other way to solve for anything.)

Here is my work..
http://imageshack.us/a/img853/9774/qmproblem2.jpg

I was able to get the Energies, but I now have nothing left to solve for A and B! I was thinking of setting ψ(0)=0 or ψ(a)=0 but I don't know if this is correct because it is the same as the non-periodic condition.
 
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  • #2
Hi.
A box is bended so that point x=0 and point x=a coincide. derivatives and value of wave function coincide there. That might be an interpretation for your question.
 
  • #3
The norm of the wave function must be 1. This is the missing condition.
 
  • #4
I did the normalization and came to the following...
[tex]A=\sqrt{\frac{2}{a}-B^2}[/tex]

I still need one more condition to solve for A and B...
 
  • #5
You have two unknowns, A and B. You have two equations relating them with each other and a. I do not think you need anything else.
 
  • #6
There are three unknowns: A, B, and k. You might find it easier to understand if you write the solution in the form ##\psi(x) = A \cos(kx+\phi)##. The normalization condition will allow you to solve for A, and like before, periodicity allows you to solve for k.
 

Related to Quantum Mechanics: Particle in a Box Periodic BC's

1. What is a particle in a box with periodic boundary conditions?

A particle in a box with periodic boundary conditions is a model used in quantum mechanics to study the behavior of a particle confined to a one-dimensional box with infinitely high potential walls. The periodic boundary conditions refer to the fact that the wave function of the particle must be continuous at the boundaries of the box, meaning that it must have the same value at both ends of the box.

2. How does a particle in a box with periodic boundary conditions differ from a particle in a box with fixed boundary conditions?

A particle in a box with fixed boundary conditions has potential walls that are impenetrable, meaning that the particle cannot pass through them. In contrast, a particle in a box with periodic boundary conditions allows the particle to pass through the boundaries and re-enter the box from the other side, similar to a particle moving on a torus. This leads to different solutions for the wave function and energy levels of the particle.

3. What is the significance of a particle in a box with periodic boundary conditions in quantum mechanics?

The particle in a box with periodic boundary conditions is a simple but important model in quantum mechanics that allows us to study the behavior of particles in confined spaces. It helps us understand the quantization of energy levels and the behavior of wave functions in such systems, which has implications for a wide range of physical phenomena such as the electronic structure of atoms and molecules.

4. How does the size of the box affect the energy levels of a particle in a box with periodic boundary conditions?

The size of the box directly affects the energy levels of the particle in a box with periodic boundary conditions. As the size of the box increases, the energy levels become more closely spaced, meaning that the energy difference between successive levels decreases. This is known as the spacing rule and is a fundamental principle in quantum mechanics.

5. Can a particle in a box with periodic boundary conditions have an infinite number of energy levels?

Yes, a particle in a box with periodic boundary conditions can have an infinite number of energy levels. However, due to the spacing rule, the energy levels become increasingly closer together as the box size increases, making it impossible to distinguish between them at a certain point. This leads to the concept of energy bands and the continuous energy spectrum in quantum mechanics.

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