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Uniformly Charged Rod

  1. Sep 2, 2014 #1

    jls

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    1. Problem Statement
    A uniformly charged rod of length L and total charge Q lies along the x axis as shown in in the figure below. (Use the following as necessary: Q, L, d, and ke.)

    (a) Find the components of the electric field at the point P on the y axis a distance d from the origin.

    (b) What are the approximate values of the field components when d >> L?

    2. Equations
    I have a diagram and understand that E=kQ/r^2, however, I can not figure out how to define each component.

    3. Attempt
    I know that I must integrate to solve once I have defined the component, however I do not know how to define them.
    Would Ex=rsin(θ)[(kQ)/r^2] and Ey=rcos(θ)[(kQ)/r^2] be at all in the right direction?
     
    Last edited: Sep 2, 2014
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  3. Sep 2, 2014 #2

    BvU

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    Hello jls, and welcome to PF.
    Can't find a picture... or is the figure below in your book only ? In that case:
    Is the center of the rod at x=0 ? (would make things easier...)
     
  4. Sep 2, 2014 #3

    vela

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    ##E = \frac{kQ}{r^2}## only applies for a point charge. There's probably an example done in your textbook that you might find very helpful.
     
  5. Sep 3, 2014 #4

    jls

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  6. Sep 4, 2014 #5

    BvU

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    Yup. Now we set up the integral (which you already expected to be needed). We take a little chunk of rod from x to x+dx and write down the x and y components of ##\vec E## at point ##\vec P = (0, y_P)##. Is one way.

    Your Ex=rsin(θ)[(kQ)/r^2] and Ey=rcos(θ)[(kQ)/r^2] looks like an integration over ##\theta##; is fine too.

    Both cases you need to express the things that vary in terms of the integrand: r(##\theta##), Q(##\theta##) -- or rather the dQ from ##\theta## to ##\theta + d\theta##. Or express them in x and dx and let x run from 0 to L.
     
  7. Sep 4, 2014 #6

    jls

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    How do you turn that chunk (x to x+dx) into the components? I think I could figure it out if I knew what that meant..
     
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