Calculating Average Energy of a quantum state

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SUMMARY

The discussion focuses on calculating the average energy, denoted as ##\langle E \rangle##, of a quantum state represented by the wave function ##\Psi = \frac{\sqrt{2}}{\sqrt{3}}\psi _1 + \frac{1}{\sqrt{3}}\psi _2##, which is a superposition of the two lowest energy states in an infinite square well. The energy levels are defined by the equation ##E_n = \frac{n^2 \pi ^2 \hbar ^2}{2mL^2}##. Participants suggest two approaches: treating the box length ##L## as a parameter or continuing with the assumption that normalization constants may simplify the expression. The consensus leans towards the first approach, retaining parameters in the final answer.

PREREQUISITES
  • Understanding of quantum mechanics principles, specifically wave functions and superposition.
  • Familiarity with the infinite square well model and its energy quantization.
  • Knowledge of the Hamiltonian operator and its relation to energy calculations.
  • Basic proficiency in mathematical manipulation of quantum equations.
NEXT STEPS
  • Study the derivation of energy levels in the infinite square well using the equation ##E_n = \frac{n^2 \pi ^2 \hbar ^2}{2mL^2}##.
  • Explore normalization techniques for wave functions in quantum mechanics.
  • Learn about the significance of coefficients ##c_n## in quantum state superpositions.
  • Investigate the implications of parameterized solutions in quantum mechanics.
USEFUL FOR

Students and professionals in quantum mechanics, particularly those studying wave functions and energy calculations in quantum systems, will benefit from this discussion.

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Homework Statement


Given a wave function that is the super position of the two lowest energies of a particle in an infinite square well ##\Psi = \frac{\sqrt{2}}{\sqrt{3}}\psi _1 + \frac{1}{\sqrt{3}}\psi _2##, find ##\langle E \rangle##.

Homework Equations

The Attempt at a Solution


I'm not sure how to proceed with this problem. I understand that we basically need to find the coefficients ##c_n## from ##\langle H \rangle = \sum |c_n|^2 E_n##, but I'm not sure how to find ##E_n##. The energy of each state is known to be ##E_n = \frac{n^2 \pi ^2 \hbar ^2}{2mL^2}##, but without the problem giving the length of the box, I can't see how we can use this.
 
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Two possibilities:
  1. Continue with ##L## as a parameter that stays in the answer. Same for ##m, \hbar, \pi##, (There is no need for a numerical value in this exercise).
  2. Continue and perhaps some of these divide out (for example because of normalization constants)
In both cases: continue :smile:

PS my money definitely isn't on case 2 :biggrin:
 

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