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Homework Help: Nonstationary states

  1. Mar 26, 2008 #1
    Consider a particle in an infinite square well of width L. Initially, (at t=0) the system is
    described by a wavefunction that is equal parts a superposition of the ground and first
    excited states:
    Ψ(x, 0)=C[Ψ1(x)+Ψ2(x)]
    a) Find C so that the wavefunction is normalized
    b) Find the wave function at any later time t.
    c)show that the expectation value of the energy in this state is (E1+E2)/2, where E1 AND E2 ARE THE ENERGIES OF THE FIRST TWO STATIONARY STATES.

    I DID a) and b) , i don't how to do c) , could you help me
  2. jcsd
  3. Mar 28, 2008 #2


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    Homework Helper
    Gold Member

    So, if [tex]\psi(x,t)[/tex] is your wavefunction, what is the expectation value of the Hamiltonian operator?
  4. Mar 28, 2008 #3


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    Homework Helper

    p.s. you may just do it at t=0, but dont forget to prove that you *can*.
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