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Homework Help: Help finding the electric feild strength in a uniform E-field

  1. Jul 2, 2014 #1
    1. The problem statement, all variables and given/known data

    The voltage across a membrane forming a cell wall is 78.7 mV and the membrane is 8.52 nm thick. What is the electric field strength? (The value is surprisingly large, but correct.) You may assume a uniform E-field.

    2. Relevant equations


    3. The attempt at a solution

    E=-(.00787V(8.52e-9m)) = 7.9e-11 V

    i dont understand why this is wrong?
    Last edited by a moderator: Jul 2, 2014
  2. jcsd
  3. Jul 2, 2014 #2
    The problem stated that the voltage was 78.7 mV, but you have written that down as 0.00787=7.87mV. Also check your multiplication.
  4. Jul 2, 2014 #3

    rude man

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    You should not have multiplied.
  5. Jul 2, 2014 #4


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    Gold Member

    use unit analysis. What are the units of an e field? what are the units of voltage?
  6. Jul 2, 2014 #5
    Okay, so i did E=(.0787)/(8.52e-9) to get 9237089 V/m is this correct? or should it be negative because in some of the equations im finding for this it has a negative. I feel like it should be positive though is this right?
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