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Find electric Field at a point A

  1. Jun 20, 2017 #1
    • Moved from a technical forum, so homework template missing
    EF_zpstnbig8yt.png

    Hi Guys,
    I've been learning electric field, and i want to ask about this question.


    EF net = EF1 + EF2

    my EF1 = 9 x 109 * 4 x 10-8 / (0.6)2 = 1 x 103 (From Q1)
    EF2 = 9 x 109 * 2 x 10-8 / (0.3)2 = 2 x 103 (From Q2)

    then EFnet = (2+1) x 103 = 3 x 103

    and what i get from key answer is 2.2 x 103

    and anyone can tell me what i miss ?
     
  2. jcsd
  3. Jun 20, 2017 #2

    DrClaude

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    Staff: Mentor

    The electric field is a vector quantity. What is its (vector) value at A?
     
  4. Jun 20, 2017 #3
    EF1_zpsjbw15xo9.png

    Enet = (E12 + E22)1/2

    Enet = 2.23 x 103

    do you mean like that bro ? anything wrong from my answer ?

    then for another question like this( at different point), just do this step ?
     
  5. Jun 20, 2017 #4

    DrClaude

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    Staff: Mentor

    There is a typo in the first equation, but otherwise this is correct.

    Yes. You first calculate the electric field itself, as a vector, and then calculate the magnitude of the vector to get the magnitude of the field.
     
  6. Jun 20, 2017 #5
    Thank you for your help.
     
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