Lecture 8: Polarization, Dielectrics, The Van de Graaff, More on Capacitors

author: Walter H. G. Lewin, Center for Future Civic Media, Massachusetts Institute of Technology, MIT
recorded by: Massachusetts Institute of Technology, MIT
published: Oct. 10, 2008,   recorded: February 2002,   views: 22491
released under terms of: Creative Commons Attribution Non-Commercial Share Alike (CC-BY-NC-SA)

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"Electric fields can induce dipoles in insulators.

Electrons and insulators are bound to the atoms and to the molecules, unlike conductors, where they can freely move, and when I apply an external field -- for instance, a field in this direction, then even though the molecules or the atoms may be completely spherical, they will become a little bit elongated in the sense that the electrons will spend a little bit more time there than they used to, and so this part become negatively charged and this part becomes positively charged, and that creates a dipole.

I discussed that with you, already, during the first lecture, because there's something quite remarkable about this, that if you have an insulator -- notice the pluses and the minuses indicate neutral atoms -- and if now, I apply an electric field, which comes down from the top, then, you see a slight shift of the electrons, they spend a little bit more time up than down, and what you see now is, you see a layer of negative charge being created at the top, and a layer of positive charge being created at the bottom.

That's the result of induction, we call that also, sometimes, polarization. You are polarizing, in a way, the electric charge..."

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Reviews and comments:

Comment1 Swati Roy, May 18, 2011 at 6:57 a.m.:

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Comment2 MIMO, December 7, 2011 at 9:10 a.m.:

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Comment3 Ebrahin saffari, May 27, 2014 at 5:14 p.m.:

Dear prof. Walter Lewin.
Would you please let me know how can i have the
complete text of your speech as one paragraph is brought on the top. I will appreciate very much if you help me
i hope you will help me. Thanks alot
your very truly
e. saffari

Comment4 ibrahim çetin sağında, March 14, 2015 at 4:02 p.m.:


Comment5 Walter Lewin, October 6, 2015 at 10:18 a.m.:

... will produce an electric field

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