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Homework Help: Find the magnitude of charge density for a power line

  1. Feb 15, 2017 #1
    1. The problem statement, all variables and given/known data
    The potential difference between the surface of a 2.2 cm -diameter power line and a point 1.9 m distant is 3.8 kV.
    What is the magnitude of the line charge density on the power line?
    Express your answer using two significant figures.

    2. Relevant equations
    V = (λ/2πε0)ln(2a/r)

    3. The attempt at a solution
    I simply converted some of the values to base units and got

    3800 V = (λ/2π(8.9e-12C))(2(0.022m)/1.9m) = -5.6e-8 C/m which is -56.4 nC/m. Its wrong however. I don't get what I am doing wrong with I solve for λ.
  2. jcsd
  3. Feb 15, 2017 #2


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    Homework Helper
    Gold Member
    2017 Award

    Think about whether or not the factor of 2 inside the logarithm is correct. Does "a" stand for the diameter of the wire?

    The middle expression is missing the logarithm function.
    Did you really mean to state that the middle expression equals the expression on the right? Note that if you read the entire line, you are saying that 3800 V = -5.6e-8 C/m.
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