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De broglie wavelength and energy

  1. Apr 11, 2009 #1
    1. The problem statement, all variables and given/known data
    The potential-energy function U(x) has the constant value U_0 in the interval 0 < x < L and is zero outside this interval. An electron is moving past this square barrier, but the energy of the electron is greater than the barrier height.

    If E= 6 U_0, what is the ratio of the de Broglie wavelength of the electron in the region x > L to the wavelength for 0 < x < L?

    2. Relevant equations

    λ=h/p= h/ sqrt(2mK)

    3. The attempt at a solution

    K are for x>L and K are for 0<x<L

    lamda1 / lambda 2 = sqrt(K2) / sqrt (K1) = sqrt (U_0) / sqrt (6U_0) = 1/ sqrt(6)

    anyone.. please help me to spot the mistakes.. :(
     
  2. jcsd
  3. Apr 11, 2009 #2

    Redbelly98

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    K is never equal to Uo.

    What is the relation between K, U, and total energy E ?
     
  4. Apr 11, 2009 #3
    e=k + u
     
  5. Apr 11, 2009 #4

    Redbelly98

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    Okay. So what is K when 0 < x < L ?
     
  6. Apr 11, 2009 #5
    k = e - u_0 = u_0 ????
     
  7. Apr 11, 2009 #6

    Redbelly98

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    No.

    The problem statement says E = ____ ?
     
  8. Apr 11, 2009 #7
    6 U_0

    but, then i guess E = 6 U_0 is for K x > L
     
  9. Apr 11, 2009 #8

    Redbelly98

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    E = 6 U_0 is for everywhere, all the time. Total energy is conserved, a constant, and never changes.
     
  10. Apr 11, 2009 #9
    yup.,, got it..
    thanks :)
     
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