1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Magnetic field caused by one Electron ?

  1. May 12, 2009 #1

    I have read Bio-Savar , Amper law (also maxwell) about Magnetic fields

    but all of them had I
    bio-savar :
    B = [tex]\frac{[tex]\mu[/tex]0}{4[tex]\pi[/tex]
    }[/tex] [tex]\frac{ids Sin\theta}{r2}[/tex]

    Amper :
    [tex]\int[/tex] B.ds = Iin [tex]\mu[/tex]0

    but what about a Electron moving in a line path ? how big will be its magnetic field ? it musnt be permenent though

    and what about a Electron spining around itself ? this time it must be permenant but how big what are the vectors ?

  2. jcsd
  3. May 12, 2009 #2


    User Avatar
    Science Advisor
    Gold Member

    You can still use the Biot-Savart law for a point charge. You just replace the current with the appropriate equivalence. I think the wikipedia article has the equation:


    That's for constant non-relativistic velocity though. I can't remember the equation for an arbitrary path/velocity.
  4. May 12, 2009 #3


    User Avatar

    Staff: Mentor

    For a uniformly moving charge, you can calculate the E and B fields by starting with the E field for a stationary charge, and performing a Lorentz transformation:


    The electron has a fixed intrinsic magnetic dipole moment, but the "spin" that it arises from is quantum-mechanical in nature.


    I'm not sure how much sense it makes to insert this dipole moment into the equations for the field of a magnetic dipole, because of its small size.

    Last edited: May 12, 2009
  5. May 12, 2009 #4
    I'm pretty sure the moving electron gives you exactly the type of field you get from the infinitesimal current element of Boit-Savart. You can set up a loop anywhere along the axis of symmetry and there will be a rate of increase of electric flux through this loop. The magnetic field integrated around the loop (constant field x 2pi*r) is equal to the increase of electric flux.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Similar Discussions: Magnetic field caused by one Electron ?