Infinite square well eignefunctions

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SUMMARY

The eigenfunctions for an infinite square well potential are defined as \(\psi_n(x) = \sqrt{\frac{2}{a}} \sin \frac{n\pi x}{a}\). For a particle with an initial normalized wavefunction \(\Psi(x,0) = A\left(\sin \frac{\pi x}{a}\right)^5\), the time-dependent wavefunction can be expressed as \(\Psi(x,t) = \sum_{n=1} c_{n} \psi_{n}(x) e^{iE_{n}t/\hbar}\). To find the coefficients \(c_n\), one must utilize trigonometric identities to rewrite \(\sin^5\) in terms of a sum of sine functions, facilitating the expansion in terms of the Hamiltonian's eigenstates.

PREREQUISITES
  • Understanding of quantum mechanics principles, particularly wavefunctions and eigenstates.
  • Familiarity with the infinite square well potential model.
  • Knowledge of trigonometric identities and their applications in quantum mechanics.
  • Basic understanding of time evolution in quantum systems using the Schrödinger equation.
NEXT STEPS
  • Research how to derive coefficients \(c_n\) for wavefunction expansions in quantum mechanics.
  • Study trigonometric identities relevant to quantum mechanics, particularly those involving powers of sine functions.
  • Learn about the Hamiltonian operator and its eigenstates in quantum systems.
  • Explore the implications of time evolution in quantum mechanics using the Schrödinger equation.
USEFUL FOR

Students and professionals in quantum mechanics, particularly those studying wavefunctions and time evolution in quantum systems, as well as educators looking for examples of eigenstate expansions in the context of the infinite square well potential.

stunner5000pt
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Homework Statement


The eignefunctions for a infinite square well potential are of the form

[tex]\psi_n} (x) = \sqrt{\frac{2}{a}} \sin \frac{n\pi x}{a}.[/tex]

Suppose a particle in this potnetial has an initial normalized wavefunction of the form
[tex]\Psi(x,0)= A\left(\sin \frac{\pi x}{a}\right)^5[/tex]

What is the form of [itex]Psi(x,t)[/itex]

2. The attempt at a solution
Now the given wavefunction [itex]Psi(x,0)[/itex] can be made to fit the infinite square well by making it a superposition

[tex]\Psi(x,t) = \sum_{n=1} c_{n} \psi_{n} (x) e^{iE_{n}t/\hbar}[/tex]

is that it?

it cnat be that simple...

thanks for your advice
 
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stunner5000pt said:

Homework Statement


The eignefunctions for a infinite square well potential are of the form

[tex]\psi_n} (x) = \sqrt{\frac{2}{a}} \sin \frac{n\pi x}{a}.[/tex]

Suppose a particle in this potnetial has an initial normalized wavefunction of the form
[tex]\Psi(x,0)= A\left(\sin \frac{\pi x}{a}\right)^5[/tex]

What is the form of [itex]Psi(x,t)[/itex]

2. The attempt at a solution
Now the given wavefunction [itex]Psi(x,0)[/itex] can be made to fit the infinite square well by making it a superposition

[tex]\Psi(x,t) = \sum_{n=1} c_{n} \psi_{n} (x) e^{iE_{n}t/\hbar}[/tex]

is that it?

it cnat be that simple...

thanks for your advice
yes. Just use a table of trig identities to write sin to the fifth power as a sum of sine functions of different arguments. That will directly give you the expansion in terms of the eigenstates of the Hamiltonian.

patrick
 

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