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Hillbilly Tutorial on Piezoelectric effect?

  1. May 6, 2005 #1
    "Hillbilly Tutorial" on Piezoelectric effect?

    What exactly is it about certain crystals like quartz, Rochelle salt, and certain ceramic materials, that causes the piezoelectric effect?

    How can just bending something produce a charge? How can putting a charge across it cause it to bend? That's just... weird.
    Talk about "truth being stranger than fiction".
    If it weren't for the fact that I've got a quartz watch on my wrist, if someone came to me and said "Ya know, theoretically, if you could make a crystal out of ordinary silicone and oxygen like this..., if you bent the crystal it'd produce a charge, and if you put a charge across it it'd bend." I'd tell 'em "Yeah, and if you could make dilithium crystals we could all travel faster than light too.", and yet...
  2. jcsd
  3. May 6, 2005 #2
    This one has an answer!

    Excerpted from: http://www.cis.yale.edu/ynhti/pubs/A5/vanwagner.html [Broken]

    This shape change actually affects the crystal at the atomic level causing a movement of ions, with their attendant electric charges. This motion of the electrically charged particles constitutes flow of electrons, or electricity.
    Last edited by a moderator: May 2, 2017
  4. May 7, 2005 #3


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    But why would you say that ? Accelerating to a speed faster than c is a violation of the first postulate of the special theory. What physical principle do you think the piezoelectric effect violates ?

    It does not violate charge conservation. Straining a piezoelectric crystal does not actually "produce a charge". It merely produces a separation of the existing charges giving rise to a voltage. It does not violate energy conservation. You do not get this voltage for free - you have to do work to strain the crystal.

    The only bizarre thing about piezoelectricity is in the mechanism. What happens in essense is that the (normally randomly oriented) molecular dipole moments line up along the direction of an applied strain field. This is a little hard to explain away simply, and I haven't really come across a good explanation/calculation anywhere, but it certainly does not seem all too unphysical to me. Also, it seems reasonable to me that all the piezoelectric crystals I know of are insulators.
    Last edited: May 7, 2005
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