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!

Homework Help: Surface charge of an elliptical tube

  1. Aug 18, 2013 #1
    1. The problem statement, all variables and given/known data
    An electric charge q is uniformly dispersed over a surface of elliptical tube with major and minor axis a and b. What is the surface charge density?

    2. Relevant equations

    3. The attempt at a solution
    I I know that you have to cut the tube in to thin ellipses and calculate a linear charge density for an ellipse. Than you sum the thin ellipses together to get a surface charge density of a tube. But I do not know how to calculate a linear charge density of an ellipse.
  2. jcsd
  3. Aug 18, 2013 #2
    If charge q is dispersed uniformly over a surface with area A, what is the surface charge density?
  4. Aug 18, 2013 #3
    Thank you for your quick replay voko. Ok, I see your point. Then I did not use the right word (lost in translation). I want calculate the areal charge density of an elliptic tube if we charge it and let the charge disperse on its own. I don’t think that we get the uniform charge density.
  5. Aug 18, 2013 #4
    Shall we assume that the tube is a conductor?
  6. Aug 18, 2013 #5
    Ow, of course.
  7. Aug 18, 2013 #6
    So you have a conducting tube (cylinder) whose cross-section is elliptical. The length of the tube is l, the ellipse's semi-major axes are a and b. Charge q is placed on the tube. Find the distribution of the charge on the tube.

    How would you approach this?
  8. Aug 18, 2013 #7
    The distribution along the length of the tube is uniform if we consider a very long tube. So we can calculate a linear charge density of a thin elliptic slice and simply multiply that with the length of the tube. Here is where I have a problem. How to calculate a linear charge density of an elliptic slice.

    I assume that the electric field inside is zero. Because the opposing sides of the ellipse cancel each other out. Now I don’t now haw to continue.
  9. Aug 18, 2013 #8


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

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

Have something to add?
Draft saved Draft deleted