Name: Brian R.
How does the electromagnetic force in an atom differ
from the other 3 forces, strong force, weak force and gravity?
The electromagnetic force is the only important force acting in an atom
outside the nucleus. It falls off relatively slowly with distance (like 1
over the distance squared) and so holds the electrons bound to the
nucleus. The strong force is over 100 times stronger, but acts only over
a very short distance, like a few fermis (A fermi is 10E-15 m) and so
doesn't affect the electrons hardly at all. The weak force is 10E-12
times the strength of the strong force and of zero range (!) and so
affects the electrons not at all. Gravity is something like 10E-44 times
the strength of the strong force and so is incredibly negligible.
So if you neglect everything except the electromagnetic force, you will
get almost exactly the right answer when calculating energy levels,
electron orbits, etc., in an atom.
Note: 10E-15 = 0.000000000000001. Notice that you have to move the
decimal point 15 places to the right to get 1.0.
Best, Dick Plano...
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Update: June 2012