How to convert this into eV

  • Thread starter leonne
  • Start date
  • #1
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Homework Statement


well the problem is electron moving in an infinte poentail box of dimensions.... calc all posible energy level in (eV)


Homework Equations


E=h2/8M(nx2/a2+....


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
 

Answers and Replies

  • #2
Pengwuino
Gold Member
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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.
 
  • #3
vela
Staff Emeritus
Science Advisor
Homework Helper
Education Advisor
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There are some useful combinations of the fundamental constants. If you know them, you can make calculations a lot faster.
\begin{align*}
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}
\end{align*}
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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