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Question:
I am currently teaching electricity to my fifth grade class. After explaining that electricity is a flow of electrons one of my students asked me how the electrons flowed. After directing many questions to him I narrowed his question to the following. We discussed electrons and the shell configurations, but how do those electrons get into a flow that we call electricity? What makes the electrons "jump"? I could also use some info on the process by which electrons move from atom to atom.



Replies:
Actually, the picture of electrons "bound" to atoms is really not correct for most solids, and particularly for metals. Why should not electrons be able to move wherever they please? It is a free country! And in metals, electrons really are "free" in the sense they basically spread throughout a very large area containing a very large number of atoms (the wavefunctions are "de-localized"). The problem with the "shell configurations" is that once atoms get close together, the electron "orbits" of neighboring atoms start to overlap, and instead of atomic shells what you get are "bands" of electron states, many of which are de-localized. When you apply an electric field, the electrons acquire some momentum and their occupation of these "bands" sloshes in the direction of the electric field. Think of individual electrons in the metal as spread out over a quite large area, and then starting to move in response to the electric field. There is your electricity. The "jumping" concept (while still possible - through quantum tunneling) applies only under special circumstances - most of the time we are interested, the electrons can just move continuously without any jumping.

Arthur Smith



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