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: Electric Charge and net force

  1. Oct 15, 2009 #1
    1. The problem statement, all variables and given/known data

    13 equal charges, q, are situated at the corners of a regular tridecagon. What is the net force on a test charge, Q, situated at the centre.

    2. Relevant equations

    F=k(qQ/r^2) r^

    (r^=r vector/r)

    3. The attempt at a solution

    The net force will be zero due to the symetry of the tridecagon.
  2. jcsd
  3. Oct 15, 2009 #2


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    What symmetry? Symmetry arguments work in regular polygons when you have an even number of vertices and therefore an even number of charges. Then the electric field at the centre is zero because contributions from charges cancel in pairs. Here you have an odd number of charges. They cannot cancel in pairs. Is the field at the centre still zero, though? You need to structure your argument more carefully.
    Last edited: Oct 15, 2009
  4. Oct 15, 2009 #3


    User Avatar
    Homework Helper

    No. There is no centre of symmetry.

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