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What is the wavelength of the light?

  1. Oct 27, 2012 #1
    Calculate the wavelength of the light emitted when an electron in a one-dimensional box of length 5.2nm makes a transition from the n = 7 state to the n = 6 state.
    Express your answer with the appropriate units.

    I calculated in this way:
    E = n^2*h^2/8*m*a^2
    E= (7^2-6^2)*(6.626*10^-34)^2/8*(9.1*10^-31)*(5.2*10^-9)^2
    E= 2.9*10^-20 J

    E = hc/λ
    λ = 6.85*10^-6 m

    But the answer is wrong.

    What is wrong with my calculation?
     
  2. jcsd
  3. Oct 27, 2012 #2

    Simon Bridge

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    How do you know the answer is wrong?

    It can help if you do the algebra first, then use more convenient units:$$\lambda=\frac{8(m_e c^2) L^2}{hc}\frac{1}{n_f^2-n_i^2}$$

    ##hc=1.240\text{eV$\mu$m}##
    ##m_ec^2=511\text{eV}##
    ##L=0.0052\text{$\mu$m}##
    ... give it a go.
    (Don't forget to check my algebra to get that equation.)
     
  4. Oct 28, 2012 #3
    It is the same calculation as mine.
    I did the exercise on MasteringChemistry. It only said my answer is wrong.
     
  5. Oct 28, 2012 #4

    Simon Bridge

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    But I got a different order of magnitude from you.
    Repeat the calculation ... you have misplaced a decimal point someplace.
     
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