How Does Particle Behavior Change in a Shifted Infinite Square Well?

In summary, the conversation discusses finding the probability distribution for a particle in a box with boundaries at x=L and x=3L, and the different methods for solving this problem. It is important to work with the fixed origin at a distance L to the left of the left side of the well. The solutions for this problem will be linear combinations of sine and cosine functions, unlike in the case of a box with boundaries at x=0 and x=L where the solution is a single sine function. It is recommended to try both methods and compare the results to ensure accuracy. The ground state for this new well will be a linear combination of a sin and a cos function.
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eku_girl83
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Any help is much appreciated!
 
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eku_girl83 said:
Suppose there is a particle in a box (infinite square well) in the ground state. The wall begins at x=L and ends at x=3L. I need to find the probability distribution for the particle.

I know how to work this problem for a well with boundaries at x=0 and x=L. In the new problem, since the width of the box is 3L - L = 2L, can I simply say that the box dimenstions are x=0 to x=2L?
No, because the whole idea here is to have you work with different boundary conditions! If you understand well the case from 0 to L, you should be able to do it from L to 3L.
This preserves the width and makes it much easier to use my boundary conditions to determine k (U(x) = A cos kx +B sin kx), since x = 0 makes the B sin kx term disappear.
Of course but there would be no point in asking this question if you could simply do this. The idea here is that someone has already made the choice to fix the origin at a distance L to the left of the left side of the well, You have to work with that. You then must give the wavefunctions with that choice of origin. It is not as simple as having the box between 0 and L but that`s the whole idea of the question!

There are two ways to proceed (I am not sure if your prof has a preference). You may start from scratch and impose that function is zero at L and at 3L and work out the conditions on A and B. And then you normalize. OR you may start from the already known solutions for 0 to L and shift the origin in these solutions to -L. Using trig identities you will get that the eiegnfunctions are linear combinations of sine and cosine functions instead of being pure sine.

Even better, you sould do it both ways and check that you get the same thing.
Also, how do I determine the ground state psi (x,0)? Is it Ax for O<x<L and A(L-x) for L<x<2L?

Any help is much appreciated!

? As you said above, the solutions are of the form A cos(kx) + Bsin(kx)! There is no way to get the function you just wrote as an eigenstate! You must be confusing with another problem!

For the 0 to L well, the ground state is what? A single sine function. In your new well, it will be alinear combination of a sin and a cos function!

Patrick
 

FAQ: How Does Particle Behavior Change in a Shifted Infinite Square Well?

What is the "Particle in a box problem"?

The "Particle in a box problem" is a theoretical physics problem that involves studying the behavior of a particle confined within a one-dimensional box. The particle is assumed to have no energy outside of the box and is only allowed to move within the boundaries of the box.

What is the significance of the "Particle in a box problem" in physics?

The "Particle in a box problem" is significant because it serves as a simplified model for understanding the behavior of quantum particles in confined spaces. It helps us understand the concept of wave-particle duality and the quantization of energy levels in quantum systems.

What are the assumptions made in the "Particle in a box problem"?

The "Particle in a box problem" assumes that the particle is confined within a one-dimensional box with infinitely high potential barriers, meaning the particle cannot escape the box. It also assumes that the particle has no energy outside of the box, and there are no external forces acting on the particle.

What is the mathematical solution to the "Particle in a box problem"?

The mathematical solution to the "Particle in a box problem" is a set of allowed energy states and corresponding wave functions. These energy states are quantized, meaning they can only take on certain discrete values, and the wave functions describe the probability of finding the particle at a given location within the box.

What are some real-life applications of the "Particle in a box problem"?

The "Particle in a box problem" has applications in various fields, such as quantum mechanics, solid-state physics, and nanotechnology. It helps us understand the behavior of electrons in atoms and molecules, the properties of semiconductors, and the behavior of particles in confined spaces in nanoscale devices.

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