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Strength and Direction of Electric Field

  1. Feb 5, 2013 #1
    1. The problem statement, all variables and given/known data

    What are the strength and direction of the electric field at the position indicated by the dot in the figure? Answer in component form.

    2. Relevant equations


    3. The attempt at a solution

    E(+5) = (8.99E9)(5E-9)/(0.02^2) = (1.1E5i, 0j)
    E(-5) = (8.99E9)(5E-9)/(0.02^2) = (0i, 2.8E4j)
    r(+10) = SQR(0.02^2+0.04^2) = 0.0447
    E(+10) = (8.99E9)(10E-9)/(0.0447^2) = 4.5E4
    = (4.5E4sin(26.57)i, 4.5cos(26.57)j)
    = (2.0E4i, -4.0E4j)​

    E(+5) + E(-5) + E(10) = (1.3E5i, -1.2E4j)

    Mastering Physics is telling me that this answer is wrong and I want to know where I screwed up.
  2. jcsd
  3. Feb 5, 2013 #2


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    Homework Helper
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    Your work looks good to me. I don't see any mistake.
  4. Feb 5, 2013 #3


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    Staff Emeritus
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    The problem may well be too much round-off error.

    Keep at least two extra digits for all intermediate results.

    Round-off your final result to the correct sig. dig. if whoever/whatever is grading your work is anal about such things.
  5. Feb 6, 2013 #4
    Turns out it was the comma in my vector notation. Once I removed the comma, the computer accepted it. Looks like I'm a bit rusty on that stuff. Thank you both for your help.
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