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

Help me to understand Coulomb's law.

  1. Oct 14, 2010 #1
    Coulombs law in SI system is given by 02493eed4cada450e2b59dc7f749e0f7.png
    from where does the factor 4[tex]\pi[/tex] come in.
     
  2. jcsd
  3. Oct 14, 2010 #2

    tiny-tim

    User Avatar
    Science Advisor
    Homework Helper

    hi sphyics! :smile:

    (have an epsilon: ε :wink:)

    it's because 4πε0r2 = ε0A(r), where A(r) is the surface area of a sphere of radius r

    see the pf library on Coulomb's law for more details :wink:
     
  4. Oct 14, 2010 #3
    Putting it another way you can express the constant as a straightforward k where (k is a constant of the medium) but for many problems 4 pi would appear in the final answer.By expressing the constant as 1/4pi epsilon(which of course is equal to k) the 4 pis would cancel in said problems.Take your choice as to how to express the constant but the 1/4pi epsilon option,although it may look more complicated at first sight,actually works out to be the neater option.
     
  5. Oct 14, 2010 #4
    Last edited: Oct 14, 2010
  6. Oct 14, 2010 #5
    agree with that, but why the fixation with [itex]4\,\pi[/itex] term in a law.
     
  7. Oct 14, 2010 #6
    The best example I can think of:
    The speed of light in a vacuum is given by root 1/epsilon zero* mu zero
    epsilon zero is an electrical constant of the vacuum(as you know) and mu zero a magnetic constant of the vacuum.If we expressed the constant in Coulombs law as a straightforward k then the equation giving the speed of light would be a bit busier( with its 4 pi) and arguably less elegant.Expressing the constant with the 4 pi just works out easier for the majority(not all) of the problems we do.
     
  8. Oct 14, 2010 #7

    tiny-tim

    User Avatar
    Science Advisor
    Homework Helper

Share this great discussion with others via Reddit, Google+, Twitter, or Facebook