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What is the magnitude of the electric field

  1. Jan 21, 2010 #1
    1. The problem statement, all variables and given/known data
    A cat rubs her back on the carpet, and acquires a net charge of -54.1 uC. What is the magnitude of the electric field at a distance 4.01 m from the cat?
    and
    What would the magnitude of the electric field in the previous problem be,
    if the distance from the cat were now tripled?


    2. Relevant equations
    F=kq/r^2


    3. The attempt at a solution
    F=8.9E9(54.1E-6)/4.01^2
    my answer came to 2.86E4 N/C which is wrong.

    obviously i should be able to get the second part once i understand what i am doing wrong in the first part
     
  2. jcsd
  3. Jan 21, 2010 #2
    You have calculated the force due to the electric field, not the field itself.

    I believe the eq you are looking for is:
    [tex]
    E=\frac{Q}{4\pi\epsilon_0r^{2}}
    [/tex]
     
  4. Jan 21, 2010 #3

    tiny-tim

    User Avatar
    Science Advisor
    Homework Helper

    it shouldn't :redface: … did you enter 8.5 instead of 8.9?

    (and isn't it 8.988, or just 9.0, anyway?)
     
  5. Jan 21, 2010 #4
    k so i did

    E=54.1E-6/4*3.14*8.85E-12*4.01^2 and got 2.7E4 N/C which still was wrong. what else did i do wrong?
     
  6. Jan 21, 2010 #5
    Never mind I got it. i was using the right equation, lol i guess i did just enter a number in wrong. funny cause i did it like 10 times. thanks though tiny-tim
     
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