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# energy equation help units watch

1. How can you tell if an energy equation will give you an answer in eV or Joules?
2. (Original post by jamesrichardkilby)
How can you tell if an energy equation will give you an answer in eV or Joules?
A reasonableness test is the easiest way.

Since they differ by a factor of 10^19:

If you had 10^19 J - All the energy the world used in a year.
If you had 10^19 eV = 1J - KE of a small apple after falling 1m.
If you had 3-5 eV - Energy range of a photon in the visible spectrum.

Best thing to do is to learn a few marks on the energy scale and use those to make reasonable comparisons, if something seems magnificently off the chart, odds are you are using the wrong units. Either that or you have found something worthy of publishing

This may help:

http://en.wikipedia.org/wiki/Orders_...itude_(energy)

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