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: Continuous line charge distribution

  1. May 21, 2007 #1
    A rod of length 80 cm has a uniform linear charge density of 5 mC/m. Determine the Electric Field at a point P located at a perpendicular distance 57 cm along a line of symmetry of the rod


    i don't know what i wrong..but here is what i am doing

    linecharge(change in lenght)= change in Q

    E=Kdq/r^2
    E=k*linecharge(dL)/r^2

    i drew a free body diagram and the x components cancle out so i only have to worry about y

    Ey=k*linecharge(dL)(costhea)/r^2 *costheta=height in y direction/r
    Ey=k*linecharge(dL)(h/r)/r^2

    so now i am going to integrate only half of the rod becuase of symetry

    so i have the integral from 0 to L/2 of k*linecharge(dL)(h/r)/r^2

    i simplify and i have Ey=k*linecharge(h) integral from 0 to L/2 of 1/r^3

    i simplify again to get =k*linecharge(L/2)/h(h^2+(L/2)^2)^1/2

    i believe this is the correct formula...but when i put the numbers in i get the wrong answer

    please help
     
  2. jcsd
  3. May 21, 2007 #2
    Hello,

    I obtain an answer that is double of yours.
    Please check your integration carefully.


    Best regards
     
  4. May 21, 2007 #3

    Dick

    User Avatar
    Science Advisor
    Homework Helper

    I get something completely different.
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook