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The magnitude of the electric field a perpendicular distance from the midpoint of the

  1. Jul 8, 2011 #1
    1. The problem statement, all variables and given/known data
    A total of 3.22 106 electrons are placed on an initially uncharged wire of length 1.29 m.

    (a) What is the magnitude of the electric field a perpendicular distance of 0.396 m away from the midpoint of the wire?


    (b) What is the magnitude of the acceleration of a proton placed at that point in space?


    3. The attempt at a solution

    A total of 2.82 * 10^6 electrons are placed on an initially uncharged wire of length 1.34 m.
    (a) What is the magnitude of the electric field a perpendicular distance of 0.404 m away from the midpoint of the wire?

    so i did
    2.82 X 10^6 electrons X 1.6 X 10^-19 C = 4.512 * 10 ^-13 = q

    then i used E = K*q / r^2

    E = 2 integral( k*q / r^2, min .404, max .78 (the hypot))
    and got 0.00969 but the answer is 0.0128 n/C

    mmm a little offf any suggestions?


    (b) What is the magnitude of the acceleration of a proton placed at that point in space?
    Newtons famous law Force = mass*accel
    Look up the mass of a proton
    a = F/m
    does this look right?
     
  2. jcsd
  3. Jul 8, 2011 #2

    Delphi51

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    Homework Helper

    Re: The magnitude of the electric field a perpendicular distance from the midpoint of

    Your part (a) is missing a lot of detail; I can't tell if it is right without doing all the work! In Integral k*dq/r², what did you replace dq with? Say you use λ = q/1.34 as the charge density along the wire. Then dq = λ*dx would work. But your integral is now over x, so r² has to be expressed in terms of x. Also, the horizontal components of the dE vectors cancel out, so you must put in a cosine or sine to take only the vertical component. I think a diagram is required to make sense of what is vertical and what is horizontal. Did you do all that?
     
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