Energy Eigenvalue: Why is (psi)n=Asin(npix/L)?

In summary, the conversation discusses the relationship between the wavefunction and energy eigenvalue in the context of an infinite square potential well. The wavefunction describes the state of a particle, while the energy is a numerical value. The conversation also mentions that the eigenstates of the Hamiltonian for the potential well are given by the wavefunction, and the energy eigenvalue can be found using a specific equation. It is also clarified that eigenfunction and eigenstate are interchangeable terms in physics.
  • #1
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why is (psi)n=Asin(npix/L) the energy eigenvalue?
 
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  • #2
It is definitely not!

What you wrote down is a wavefunction which describes the state of a particle, not an energy, which is ofcourse a number. Also, this is an eigenstate of the Hamiltonian for an infinite square potential well, which you failed to mention that at all. The eigenstates depend on the potential energy function.

So for the infinite square potential well the eigenstates of the Hamiltonian (socalled stationary states) are give by the wavefunction you wrote down. The energy eigenvalue E_n corresponding to psi_n can for example be found by:
[tex]\hat H \psi_n = E_n \psi_n[/tex]
 
  • #3
This sgould correspond to the bound state in a square well of length L. The energy inside the (i think) infinite wall shoule be given simply by the second derivative times -hbar^2, hence : the energy eingenvalue should be : En=n^2*pi^2/L^2*hbar^2...
 
  • #4
um, I've heard about eigenvalues and eigenfunctions, but this is the first I'm heard about an eigenstate! what's that?
 
  • #5
Eigenfunction and eigenstate is the same thing.
In physics we like to refer to the system as being in a 'state' rather than an abstract mathematical entity such as function. Please don't get confused.
 
  • #6
thank you very much! :)
 

Related to Energy Eigenvalue: Why is (psi)n=Asin(npix/L)?

1. What is an energy eigenvalue?

An energy eigenvalue is a value that represents the energy of a specific state or level of a quantum mechanical system. It is a fundamental concept in quantum mechanics and is used to describe the behavior and properties of particles at the atomic and subatomic level.

2. How is the energy eigenvalue represented in the equation (psi)n=Asin(npix/L)?

The energy eigenvalue is represented by the variable n in the equation. It is multiplied by the constant h (Planck's constant) and divided by the wavelength of the particle (λ) to calculate the energy of a particular state.

3. Why is the wave function (psi) represented as a sine function in the energy eigenvalue equation?

The wave function (psi) represents the probability amplitude of a particle being in a specific state. In quantum mechanics, particles are described as waves, and the sine function is a common wave function used to describe the behavior of particles in a confined space.

4. What is the significance of the constant A in the energy eigenvalue equation?

The constant A in the energy eigenvalue equation represents the amplitude of the wave function. It is a normalization constant that ensures the probability amplitude is always between 0 and 1.

5. How does the length of the box (L) affect the energy eigenvalue equation?

The length of the box (L) is a crucial factor in determining the energy eigenvalues of a system. As the length of the box changes, the allowed energy levels of the system also change. This is because the standing waves inside the box must have an integer number of half-wavelengths to satisfy the boundary conditions, resulting in different energy eigenvalues.

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