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Homework Help: How to convert this into eV

  1. Oct 28, 2011 #1
    1. The problem statement, all variables and given/known data
    well the problem is electron moving in an infinte poentail box of dimensions.... calc all posible energy level in (eV)

    2. Relevant equations

    3. The attempt at a solution
    ok so no idea how they get h2/8M to = 37.6 h is planks constant the units are in m4kg s-2 but eV is in m2kg s-2 dont see how they get 37.6 for mass i used 9.11e-31
  2. jcsd
  3. Oct 28, 2011 #2


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    Gold Member

    Find out the energy levels in Joules and simply use the conversion between Joules and eV. Should be easily google'd/wikipedia'ed or should be in your textbook.
  4. Oct 28, 2011 #3


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    There are some useful combinations of the fundamental constants. If you know them, you can make calculations a lot faster.
    h c &= 1240~\text{eV nm} \\
    \hbar c &= 197~\text{eV nm} = 197~\text{MeV fm} \\
    m_e c^2 &= 511000~\text{eV} = 511~\text{keV} = 0.511~\text{MeV}
    For your problem, you just need to introduce factors of c, the speed of light, to form the right combinations:
    [tex]\frac{h^2}{8m} = \frac{(hc)^2}{8mc^2} = 0.376~\text{eV nm}^2[/tex]Note that this combination has two powers of length. They are needed to cancel the units from a2 in the denominator of the formula for the energy.
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