Strength and Direction of Electric Field

  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.
    [​IMG]

    2. Relevant equations

    E=kQ/r^2

    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
    arctan(2/4)=26.57DEG
    = (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. TSny

    TSny 5,644
    Homework Helper
    Gold Member

    Your work looks good to me. I don't see any mistake.
     
  4. SammyS

    SammyS 8,061
    Staff Emeritus
    Science Advisor
    Homework Helper
    Gold Member

    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. 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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