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Electrons at rest have magnetic fields

  1. Jun 20, 2015 #1
    It could be that I'm misinformed, but I heard electrons at rest have magnetic fields. I thought that magnetic fields required a charge to be traveling at velocity before a magnetic field would arise. If this is the case could someone help me out?

    If an electron has a magnetic field at rest what is its strength? Or to be more specific, if we were to take the classical radius of the electron, 2.8179403267 x 10^-15m, what would the surface force due to magnetism be on the electron if we could somehow shrink ourselves to that size and stand on the electron's surface? Is there anyone who can calculate what that value would be assuming what I heard was correct?
     
    Last edited: Jun 20, 2015
  2. jcsd
  3. Jun 20, 2015 #2
    Electrons have a property called "spin".
    With this comes a magnetic dipole moment, so an electron is a tiny permanent magnet.
    Its magnetic moment has a value of about 10^-23 J/T (Bohr magneton).
     
    Last edited: Jun 20, 2015
  4. Jun 20, 2015 #3

    Dale

    Staff: Mentor

    Electrons have spin angular momentum and charge, so they do have an intrinsic magnetic dipole moment.

    The classical radius thing is meaningless for an electron so there isn't a good answer for your other questions.
     
  5. Jun 20, 2015 #4
    I see guys, thanks. So electrons are like little magnets then. Is there any way to calculate their magnetic field strength?
     
  6. Jun 20, 2015 #5

    Dale

    Staff: Mentor

    Certainly. Here is a good starting point for an overview. https://en.m.wikipedia.org/wiki/Electron_magnetic_moment
     
  7. Jun 26, 2015 #6
    I've got one more question concerning what was brought up here. If electrons are like tiny magnets with two poles of different polarity why do we view them as charged particles? Maybe there is something here I'm not quite grasping. Here's my thinking, an electron has a negative charge of roughly 1.6x10^-19 C. However, it must also have two poles of opposite polarity(like say the earth). Why don't these poles cancel out and give us a neutral particle? Is there something here I'm misunderstanding?
     
  8. Jun 26, 2015 #7

    Dale

    Staff: Mentor

    You seem to be mixing up magnetic poles and electrical charge. An electron has a monopolar electric field and a dipole magnetic field. Therefore it has an electric charge but not a magnetic charge (magnetic charges don't exist as far as we can tell).
     
  9. Jun 26, 2015 #8
    Thank you for your reply Dalespam.

    If magnetic fields don't have charge then why can we write a Beta field equation as , B=μ0/4π(Q/r2) where: Q= the charge of the field? Which again is the analog in magnetism of Coulomb's law?
     
  10. Jun 26, 2015 #9

    Dale

    Staff: Mentor

    That equation is not correct. Where did you get it?

    Magnetic fields are caused by moving electric charges (electric current), not by separate magnetic charges.
     
  11. Jun 26, 2015 #10
    The equation came from Coulomb, the same guy who gave us Coulomb's law F=k(q1q2/r^2).

    The law of force between poles was investigated by Charles Coulomb, using the same torsion balance with which he established the law of force between electric charges, and was found to be similar in form to that for charges.

    In coulomb's law the the constant of proportionality was found to be k coulomb's constant which is the permittivity of free space. In the other equation the constant of proportionality was found to be μ0/4π the permeability of free space.
     
  12. Jun 26, 2015 #11

    Dale

    Staff: Mentor

    Please provide a specific reference for this equation.

    Do you understand the difference between a monopole and a dipole? Gauss law for magnetism prohibits monopolar magnetic sources, but Gauss law permits monopolar electric sources. Thus the electron has electric charge (monopolar), and a magnetic moment (dipole).
     
    Last edited: Jun 26, 2015
  13. Jun 26, 2015 #12
    Here's a quick link.
    http://www.daviddarling.info/encyclopedia/C/Coulombs_law_for_magnets.html
     
  14. Jun 26, 2015 #13
  15. Jun 27, 2015 #14

    Dale

    Staff: Mentor

    Read the third paragraph on that page. It confirms what I was saying.

    Note also paragraph four which describes how the following information uses long thin magnets as shown in the figure. An electron is, to the best of our measurements, a point dipole. So the subsequent equations don't apply.
     
    Last edited: Jun 27, 2015
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