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Homework Help: Electrostatic field ( Gauss Law )

  1. Apr 24, 2009 #1
    1. The problem statement, all variables and given/known data
    Assuming that an infinitely long line charge of 50(pC/m) parallel to the y-axis at x=2(m) and z=1(m), determine the electric intensity at the point (-1, 5, -3).

    The answer given : -0.18(ax0.6 + az0.8)(V/m)

    2. Relevant equations
    Electric field intensity due to an infinite straight line charge of uniform density :
    E= ar("rho" / (2"pi""epsolon 0"r) ( V/m)

    3. The attempt at a solution

    I let point P = -ax + ay5 - az3
    Point on line perpendicular to point P, Q = ax2 + az

    Vector Q to P = -ax3 + ay5 - az4

    I found out that if i ignore or make coefficient of ay to zero and apply the above formula i'll get the answer..

    but i do not understand why..please help
    Last edited: Apr 24, 2009
  2. jcsd
  3. Apr 24, 2009 #2


    User Avatar
    Homework Helper
    Gold Member

    Hi Saru,

    Draw a picture and you will see the reason immediately. You are not looking for the distance from P to Q, but from P to the line of charge.
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