Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Fundamental problem in electrostatics

  1. Feb 19, 2007 #1
    Can someone say why it is said that in electrostatics,the test charge may be moving very slowly?Specifically,what is wrong if the test charge moves at a speed which is a significant proper fraction of speed of light?
     
  2. jcsd
  3. Feb 19, 2007 #2
    From my little understanding... (warning: which could be wrong )
    When you move a charge you create current, which creates a magnetic field, which creates an electric field. The calculation becomes messy. Plus, electrostatics doesn't worry itself with time-varying fields. Also moving a significant fraction of the speed of light then brings in relativistic effects.
     
  4. Feb 19, 2007 #3
    I see.Let me concretize:
    In electrostatics,we neglect magnetic effects and time varying effects.Now,a single moving charge,even running at a constant speed,results in a non-steady current,and that in turn,will result in a time-varying magnetic field.This,again,will induce a time varying electric field.
    Now,if the speed is very small,we will have a slight fluctuation and if the speed is high,the magnitude of current,and hence,the resulting E and B fields will be big.So,electrostatics will make a mess with big fluctuations in fields and magnetic effects.
     
  5. Feb 19, 2007 #4
    If people would use CGS or Gaussian units, it would be apparent that the magnetic effects are proportional to v/c, so it's a very small effect indeed. Thus, "slowly" basically means "a negligible fraction of the speed of light".
     
  6. Feb 19, 2007 #5
    Yes!Of course.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?