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Electric field strength -- calculating distance from charge

  1. Feb 22, 2017 #1
    1. The problem statement, all variables and given/known data
    At a distance D from a very long (essentially infinite) uniform line of charge, the electric field strength is 1000 N/C. At what distance from the line will the field strength to be 4000 N/C?

    2. Relevant equations
    E=kq/r2

    3. The attempt at a solution
    I know that E is inversely proportional like so: E~1/r2
    hence by rearranging for 'r' I got: r~sqrt(1/E)
    then I plugged in 4E because 4000 N/C is four times 1000 N/C: r~sqrt(q/4E)
    and I got r~E/2 but the answer is E/4 and I don't know how?

    Thanks in advance
     
  2. jcsd
  3. Feb 22, 2017 #2

    BvU

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    Science Advisor
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    Gold Member

    HI,

    You want to develop an expression for the electric field of a long line charge first. Your relevant equation doesn't fit that.
     
  4. Sep 12, 2017 #3

    Fab

    User Avatar

    What is the relevant equation that fits this scenario then?
     
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