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Field due to ring of charge

  1. Jul 2, 2017 #1
    1. The problem statement, all variables and given/known data
    A uniform circular ring of charge Q=4.20 microCoulombs and radius R=1.30 cm is located in the x-y plane, centered on the origin as shown in the figure.

    What is the magnitude of the electric field E at point P, located at z=3.70 cm?

    I have worked out the problem and got the following formula which I know is correct but when I enter in my numbers it doesn't seem to give me the correct answer, so I'm wondering what I am doing wrong (see below)

    E_z = (kQx)/((x^2+R^2)^(3/2))

    where k=9x10^9, Q = 4.2*10^-6, x= 0.0130, and R = 0.0370.

    2. Relevant equations


    3. The attempt at a solution
    I have worked out the problem and got the following formula which I know is correct but when I enter in my numbers it doesn't seem to give me the correct answer, so I'm wondering what I am doing wrong (see below)

    E_z = (kQx)/((x^2+R^2)^(3/2))

    where k=9x10^9, Q = 4.2*10^-6, x= 0.0130, and z = 0.0370.

    So what am I doing wrong? are my numbers above correct? fuck.jpg fuck.jpg

    2.316×10^7 N/C
     
    Last edited: Jul 2, 2017
  2. jcsd
  3. Jul 2, 2017 #2

    rcgldr

    User Avatar
    Homework Helper

    Looks like you swapped constants. This could be avoided if you restated the equation as

    E_z = (kQz)/((z^2+R^2)^(3/2))

    R = .0130 m
    z = .0370 m
    ...
     
  4. Jul 2, 2017 #3

    thanks that fixed my problem!


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