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What causes the electron to orbit the nucleus? Which is the force that causes it to do so? Is it related to the Electro - Magnetic force? .

Abhimanyu Pallavi Sudhir
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APARAJITA
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    Hi Aparajita, please specify your doubt? What do you believe? Electrodynamics is a field, do you mean electrostatics coulomb force? If yes, then you are right, it is electrostatics coulomb force that provides necessary centripetal force to electron for circling around the nucleus. – orionphy Aug 25 '13 at 13:36
  • I meant electrostatic force, I actually wanted to ask why do electrons move at all? What makes them move? – APARAJITA Aug 25 '13 at 13:48
  • Consider this, an electron that is away from the positive nucleus (i.e. which is not part of the atom) gets attracted toward it due to electrostatics force. – orionphy Aug 25 '13 at 13:59
  • Than you Orion, but what gives them the speed? Is it electrostatic force again? – APARAJITA Aug 25 '13 at 14:06
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    Quantum physical rules does not allow it to fall inside nucleus and hence it starts orbiting around it. When it started orbiting in the nth orbit, it had the angular momentum $n\hbar$. It keeps on orbiting due to conservation of angular momentum. – orionphy Aug 25 '13 at 14:07
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    Related: http://physics.stackexchange.com/q/9415/2451 and links therein. – Qmechanic Aug 25 '13 at 15:39
  • This was not the question asked by me, it has been edited – APARAJITA Aug 29 '13 at 17:22

1 Answers1

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It doesn't actually orbit the nucleus in the modern quantum mechanical understanding of the atom, although in a classical approximation, some properties relating to electron energy levels, etc. can be reproduced in terms of the picture of an "orbiting electron"*.

The reason you have an orbiting electron in the classical model is also related to this, as the only way the classical model can (try to) explain a stationary point-electron that isn't collapsing into the nucleus is to say the electron is spinning really fast. Note that "classical" in this sense also includes the Bohr model, which is entirely classical except it follows the old quantum rule $\int p\,dq=n\hbar$.

*as an example -- the energy levels in a quantum atom are given as $\sqrt{1-\alpha^2Z^2}$ where the fine structure constant $\alpha\approx1/137$, which is why you don't have atoms with more than 137 electrons. But in the classical picture, this gets re-interpreted as saying "the outer electron will have to move faster than light if you get more than 137 electrons", which has the same impact on the real-ness of the energy level.

Abhimanyu Pallavi Sudhir
  • 6,140