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Homework Help: Electric field and rectabgle

  1. Jan 21, 2009 #1
    1. The problem statement, all variables and given/known data
    Three positive charges are arranged in a rectangle. The charge in the bottom left corner is +5.63 nC, in the top left corner is +5.64 nC, and in the bottom right corner it is +11.28 nC. The sides have a length of 0.639 m and .213 m. Find the magnitude of the electric field at the fourth corner of the rectangle. Answer in units of N/C.

    2. Relevant equations
    E = kq / r^2

    3. The attempt at a solution
    E for bottom left : k(q) / (.67356m)^2 = 111.53 N/C

    E for top left : kq/ (.213m)^2 = 1117.28 N/C

    E for bottom right : kq / (.639m)^2 = 248.284 N/C

    Then I drew these Electric fields on an x-y axis and they all ended up in quadrant one. So I then found the x an dy components of each. Ex total was 1196.14 and Ey total was 327.148
    Finally I found the Electric field for 4th corner by using the x and y compoenents and it turned out to be 1240.07 N/C .
    for some reason Im not wholly assured that my answer is correct. Can you please look over and tell me if there is anything wrong with my problem solving approach. Thank you very much =]
  2. jcsd
  3. Jan 21, 2009 #2
    sure enough I entered the answer and it was wrong =( . I am now in dire need of help
  4. Jan 21, 2009 #3


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    Homework Helper
    Gold Member

    Good :smile:
    That's not what I get. Perhaps you should show me what you are getting for the x and y components of the field from the bottom left charge.
  5. Jan 21, 2009 #4
    Thank you for cheking my work . My approach was correct. The way I had drawn my diagram of the charges was incorrect, which led me to make some false assumptions. For example I was using 45 degrees as my angle when i was finding components. However that is incorrect because the figure is a rectabgle not a square so instead I had to use the ratios of the sides in order to calculate my components.
    Thank you once again!
  6. Jan 21, 2009 #5


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    Homework Helper
    Gold Member

    Welcome :smile:
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