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Electric field problem

  1. Nov 9, 2015 #1
    1. The problem statement, all variables and given/known data
    The potential at a point x(measured in µm)due to some charges situated on the x axis is given by ##V(x)##=##\frac{20}{x^2-4}##V.The electric field ##E## at x=4µm is ?
    2. Relevant equations
    ##E##=-##\frac{∂V}{∂r}##

    3. The attempt at a solution
    Actually I have solution but still I am unable to understand.So ,instead of my attempt at a solution .I 'll post solution itself.
    ##Ex##=-##\frac{∂V}{∂x}## (1)

    = -##\frac{d}{dx}(\frac{20}{x^2-4})## (2)

    =##\frac{40x}{(x^2-4)^2}## (3)

    ##Ex## at x=4µm =##\frac{10}{9}##V/µm
    Here I am not able to understand how it proceeded from (2) to (3)
     
  2. jcsd
  3. Nov 9, 2015 #2

    blue_leaf77

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  4. Nov 9, 2015 #3
    And how to proceed from (3) to answer?
     
  5. Nov 9, 2015 #4

    blue_leaf77

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    You just plug in x=4 into the expression, right?
     
  6. Nov 9, 2015 #5
    Yes,of course.
     
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