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Homework Help: Electric Field in 3 Parallel Plates

  1. Mar 13, 2013 #1
    1. The problem statement, all variables and given/known data
    What is the electric field at point A in the unit of σ/ε0?

    2. Relevant equations

    3. The attempt at a solution
    I just want to make sure my thinking behind this is correct.
    From the center we have +5σ. To find the A what I did is subtract the other two -σ from the 5: this gives me 5-1-1 = 3.
    From here I just plug in: 3σ/2ε which in the units = 1.5 σ/ε

    Is this the correct approach?

    Attached Files:

  2. jcsd
  3. Mar 13, 2013 #2


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  4. Mar 13, 2013 #3

    rude man

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    Alternative sol'n: if you put a Gaussian box of area = 1m^2 and running from A to D, the inside net free charge is 3σ C and the total flux area is 2 m^2 (no flux out the other 4 sides if the plates are infinite in dimension).

    That would make εE*2m^2 = 3σ so E = (3/2)σ/ε. Same answer!
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