# Coulomb Energy Units

1. Apr 22, 2012

### atomicpedals

I'm having some difficulty resolving the units (unit conversions will be my great un-doing) for calculation of the Coulomb energy between nuclei. Given that

$$\Delta E = \frac{3e^{2}}{5r} (2Z-1)$$

with the value for r in fermis (~10^-13cm), the elementary charge e in coulombs, and Z is dimensionless. How can I resolve this into MeV? Or can I?

The problem which brought this on is to compare the difference in rest mass with the Coulomb energy. With the rest mass being in MeV it would seem that I would need the Coulomb energy in similar units, but I'm just not seeing how to do it.

Last edited: Apr 22, 2012
2. Apr 22, 2012

### atomicpedals

I've found a reference to the coefficient with e and r being 0.807MeV. While that's useful for completing the problem-set it leaves me a bit unsatisfied as far as explanations go.

3. Apr 22, 2012

### tiny-tim

hi atomicpedals!
eV is not an SI unit,

so you'll have to use eV = 1.602 10-19 J

4. Apr 22, 2012

### atomicpedals

...*face-palm*

Yep... and that does it. Thanks!