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Question about electirc field

  1. Mar 14, 2013 #1
    In my book it says that the electric field (E) is equal to the following

    E = -dV/dx <0
    where V = Volatage and x = position

    However if you look in the paint doc on one of my homework problems you will see that
    E>0

    They say that E = dV/dx = Δv/Δx (where Δx = d).
    So E = Δv/Δx > 0 (because E is UNIFORM therefor dV/dx = Δv/Δx)


    Questions:
    1. When should I use the equation E = -dV/dx?
    2. Why did they not use E = -dV/dx?
    3. Is E a vector in this equation? Hence the neg sign indicates direction
     

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  3. Mar 14, 2013 #2

    SammyS

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    I believe in this case they are using "E" as the magnitude of the electric field.
     
  4. Mar 15, 2013 #3

    rude man

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    Always.

    But the real equation is E = - del V where
    del V = ∂V/∂x i + ∂V/∂y j + ∂V/∂z k
    where i , j and k are unit vectors in x,y,z direction resp.

    Reason: the E field may point in a direction with x, y and/or z components, not just x.
     
    Last edited: Mar 15, 2013
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