Momentum eigenvalues and eigenfunctions

In summary, the given wave functions are shown to be eigenfunctions of Lx, Ly, and Lz as well as L^2 by explicitly calculating the corresponding partial derivatives and using the given equations. The corresponding eigenvalues are also found. However, the solution may be simplified by using the fact that L^2 is the sum of Lx^2, Ly^2, and Lz^2.
  • #1
White_M
9
0

Homework Statement



For the following wave functions:
ψ[itex]_{x}[/itex]=xf(r)
ψ[itex]_{y}[/itex]=yf(f)
ψ[itex]_{z}[/itex]=zf(f)

show, by explicit calculation, that they are eigenfunctions of Lx,Ly,Lz respectively, as well as of L^2, and find their corresponding eigenvalues.

Homework Equations



I used:
L[itex]_{x}[/itex]=-ih(y[itex]\partial/\partial z[/itex]-z[itex]\partial/\partial y[/itex])
L[itex]_{y}[/itex]=-ih(z[itex]\partial/\partial x[/itex]-x[itex]\partial/\partial z[/itex])
L[itex]_{z}[/itex]=-ih(x[itex]\partial/\partial y[/itex]-y[itex]\partial/\partial x[/itex])

for solving:

L[itex]_{z}[/itex]|ψ[itex]_{z}[/itex]>=lz|ψ[itex]_{z}[/itex]>
L[itex]_{x}[/itex]|ψ[itex]_{x}[/itex]>=lx|ψ[itex]_{x}[/itex]>
L[itex]_{y}[/itex]|ψ[itex]_{y}[/itex]>=ly|ψ[itex]_{y}[/itex]>


and
L^2|ψ>=l^2|ψ>

where:
L^2=L[itex]_{x}[/itex]^2+L[itex]_{y}[/itex]^2+L[itex]_{z}[/itex]^2

The Attempt at a Solution



For instance for Lz:
ψ[itex]_{z}[/itex](r)=<r|z>=zf(r)

L[itex]_{z}[/itex]|ψ[itex]_{z}[/itex]>=-ih(x[itex]\partial/\partial y[/itex]-y[itex]\partial/\partial x[/itex]) zf(r)=lz|ψ[itex]_{z}[/itex]>

Is that correct?
 
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  • #2
I think they want you to "explicitly" take partial derivatives of the function z f(r) .
 
  • #3
-ih (x([itex]\partial[/itex]z\[itex]\partial[/itex]y f(r)+z [itex]\partial[/itex]f(r)/[itex]\partial[/itex]y)-y([itex]\partial[/itex]z\[itex]\partial[/itex]x+z[itex]\partial[/itex]f(r)\[itex]\partial[/itex]x))=-ih (xz[itex]\partial[/itex]f(r)\[itex]\partial[/itex]y-yz [itex]\partial[/itex]f(r)\[itex]\partial[/itex]x)=-ih (x[itex]\partial[/itex]\[itex]\partial[/itex]y-y[itex]\partial[/itex]\[itex]\partial[/itex]x)zf(r)

Which is the same as the initial expression.

What am I missing?

Thanks
 

1. What are momentum eigenvalues and eigenfunctions?

Momentum eigenvalues and eigenfunctions are mathematical concepts used to describe the momentum of a quantum particle. The momentum eigenvalue represents the possible values of momentum that a particle can have, while the eigenfunction describes the probability amplitude of finding the particle with a specific momentum value.

2. How are momentum eigenvalues and eigenfunctions related?

Momentum eigenvalues and eigenfunctions are related through the momentum operator, which is a mathematical operator that acts on the wavefunction of a quantum particle to give its momentum eigenvalues and eigenfunctions. The eigenfunctions are the eigenvectors of the momentum operator, and the eigenvalues are the corresponding eigenvalues.

3. What is the significance of momentum eigenvalues and eigenfunctions in quantum mechanics?

Momentum eigenvalues and eigenfunctions play a crucial role in quantum mechanics as they provide a way to describe and understand the behavior of quantum particles, which do not behave like classical particles. They also allow us to make predictions about the outcomes of measurements of a particle's momentum.

4. How do you calculate momentum eigenvalues and eigenfunctions?

Momentum eigenvalues and eigenfunctions can be calculated using the Schrödinger equation, which is a fundamental equation in quantum mechanics. The momentum eigenvalue is given by the momentum operator acting on the wavefunction, and the eigenfunction is the solution to the Schrödinger equation with the corresponding eigenvalue.

5. Can momentum eigenvalues and eigenfunctions change over time?

Yes, momentum eigenvalues and eigenfunctions can change over time. This is because the wavefunction of a quantum particle evolves over time according to the Schrödinger equation, and the momentum eigenvalues and eigenfunctions are dependent on the wavefunction. As the wavefunction changes, so do the momentum eigenvalues and eigenfunctions.

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