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Homework Help: Electric field intensity around a wire

  1. Sep 10, 2014 #1
    1. The problem statement, all variables and given/known data

    I am trying to calculate the surface charge density and electric field intensity around a copper wire. This is not a part of my assignment but out of curiosity. First, A current carrying wire of radius 2m, radius 0.5cm is at a height of 5cm above a ground plane, the ground plane is at a potential of 24V, the wire is at a potential of say 12V. How do I calculate the e.field intensity and surface charge density around the wire?

    if a large current (like lightning) of 10KA having charge of 26C, and frequency 100Hz flows through the wire. what would be the charge on the wire and How would it effect the potential since (V=I*R)?

    2. Relevant equations
    The charge density ρ=(q/A)
    Efield intensity E=λ/(2∏ε0*R)
    where R is the radius of the gaussian surface, λ is the charge per unit length

    3. The attempt at a solution
    Attributing the wire to be a cylinder; the surface area would be A=2∏rh+2∏(r^2) = 0.0629 m2.
    here h = length of the wire.
    To get the value of q for surface charge density.(I know I'm wrong)
    q = I*t
    t= 1/f = 1/100 = 10ms; I = 10KA
    q = 100C
    charge density ρ= 1.5K C/m2 ??

    to solve E.field intensity, I considered a gaussian surface with the distance between the wire and ground plane as the radius R and the length of the gaussian surface equal to the length of the cylinder
    if the lightning carriers charges of 26C then λ= 26/2 = 13 (assuming uniform distribution of charge on surface)
    E = 13/(2∏*ε0*2)
    E = 0.1*10^-12 V/m??

    I'm Extremely confused. Any help will be really appreciated.
  2. jcsd
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