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Why don't electrons jump between the turns of a coil?

  1. Dec 19, 2015 #1
    Hey guys. I just want to know why electrons in a coil always follow the turns instead of jumping from one turn to another. I mean, in many cases the turns are very close to one another. Also, if I'm not mistaken, electrons travel the shortest distances. Thank you!
     
  2. jcsd
  3. Dec 19, 2015 #2

    jtbell

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    The wire has insulation on it. If it didn't, you would indeed have a "short circuit" between the turns of a coil, if they're in contact.
     
  4. Dec 19, 2015 #3

    Averagesupernova

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    Sometimes they do. Usually this is not considered a good thing. Lightning is usually thought of as 'not liking corners'. It contains very high frequencies and sometimes the inductance is high enough to cause arcing between turns when a coil is involved in lightning strikes.
     
  5. Dec 19, 2015 #4

    dlgoff

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    It's all in their speed. Not fast enough to jump that far. Here's a neat little video about their speed.

     
  6. Dec 20, 2015 #5

    davenn

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    not completely
    it's more their electron volt potential. if the voltage potential is enough to break down the insulation / air-gap
    they will indeed jump between turns


    Dave
     
  7. Dec 20, 2015 #6

    meBigGuy

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    I don't understand any of the answers so far.
    That is very mistaken.

    The electrons take the path of least resistance, not the shortest path. The path traveled is that which requires the least expended energy.

    Wire has high conductivity, insulation does not. You can read about the causes of conductivity here:
    https://en.wikipedia.org/wiki/Electrical_resistivity_and_conductivity

    It requires more force to travel through materials with lower conductivity (the wire insulation) so the electrons travel the long way around to "save energy".
     
  8. Dec 20, 2015 #7

    dlgoff

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    Well yes. The point I was trying to make is, there's not enough energy (hence velocity) to cause breakdown; as @meBigGuy explains via conductivity. The phenomenon of arcs needs high electron volt potentials to occur.

    Quote taken from http://www.physics.csbsju.edu/370/jcalvert/dischg.htm.html#Arc

    I did an image search trying to find a coil showing any kind of arcing across turns and couldn't find any. I wonder why? :devil:
     
  9. Dec 20, 2015 #8

    rbelli1

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    No, no, no, no. The electrons take all paths inversely proportional to the resistances of those paths.

    If the quote were true than only one electrical device would ever be able to be connected to any given generating station and only one component in that device would be operational.

    In reality some current is flowing through the insulation but the resistivity of the copper is so much lower than the plastic insulation that that current may be ignored.
    Bulk resistivity of copper 0.000000017
    Bulk resistivity of Mylar 10000000000000000000, which is similar to the insulation materials used on magnet wire.

    BoB
     
  10. Dec 20, 2015 #9

    davenn

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    yes that's correct voltage levels were not initially mentioned, and velocity doesn't enter into it ;)
    the energy of an electron can be very high but its velocity can be zero ... consider a charge on a capacitor that breaks down the dielectric

    In the context of the OP, I was just stating that under the under the right voltage potentials arcing between turns is possible :smile:

    Dave
     
  11. Dec 20, 2015 #10
    Ok so if the potencial is enough then electrons can actually get through air gaps or even the insulation of the fabric that covers the wire. However, most coils I've seen don't seem to have anything covering up the wire. Do they still possess insulation?
     
  12. Dec 20, 2015 #11

    meBigGuy

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    Of course that is correct. I oversimplified to the point of being incorrect. In the case with the coil there will be a small current through the insulation (all possible paths). The bulk of the current (in this case) will flow through the metal wire path with least resistance.
     
  13. Dec 20, 2015 #12

    meBigGuy

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    Most coils have an insulating enamel coating (google "magnet wire"). If it is not insulated, it will be wound on a grooved forms that separates the windings.
     
  14. Dec 20, 2015 #13
    The insulation around the wire of the coil makes the 'path of least resistance' the wire, but a coil or inductor stores the current as a magnetic field around the coil and the energy (of the electrons) in that magnetic field influences all the other coils (or loops) in the coil. But if you have two conductors close together but separated by an insulator then that is a capacitor, so a varying voltage across the coil will induce change in the other loops of the coil. So the electrons themselves do not jump across loops of the coil and electric and magnetic fields do.
     
  15. Dec 21, 2015 #14
    by frequencies you mean lightning is a form of alternate current?
     
  16. Dec 22, 2015 #15

    Averagesupernova

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    Yes. This is why we hear it in radio receivers.
     
  17. Dec 22, 2015 #16
    I felt it was really good , thank you ^^~
     
  18. Dec 22, 2015 #17

    NascentOxygen

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    The insulating paint ('enamel') on the wire used for electromagnets in relays, and for inductors and transformers, is often similar in colour to copper wire, if a bit darker, so that can be why it's sometimes mistakenly thought to be bare copper. If you look inside TV sets you'll see inductors wound using bare uninsulated wire; these are wound using stiff self-supporting wire or tubing and the turns are spaced apart, so there is air insulation separating each turn from its neighbours.
     
  19. Dec 22, 2015 #18

    meBigGuy

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    I think we hear lightning in radio receivers for the same reason we hear any capacitive DC discharges in radio receivers. Lightning is a DC discharge. It is a impulse, and as such produces some high frequency RF components. Calling it AC is the same as saying that turning on a flashlight is AC because it produces high frequency components. Yes, it produces some AC components, but the basic phenomena is a DC discharge.
     
  20. Dec 22, 2015 #19

    CWatters

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    Frequently the insulation is a (semi) clear varnish or, as NascentOxygen said, it's a similar colour to copper.
     
  21. Dec 22, 2015 #20

    Averagesupernova

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    Yes I probably should have been more specific.
     
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