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Homework Help: Uniformly charged rod(exam in 3 hours, please help)

  1. Feb 8, 2013 #1
    1. The problem statement, all variables and given/known data
    A rod 11.9 cm long is uniformly charged and
    has a total charge of −17.7 μC.
    Find the magnitude of the electric field
    along the axis of the rod at a point 46.2418 cm
    from the center of the rod. The Coulomb con-
    stant is 8.98755 × 109 N · m2/C2.

    lecture problem im trying to review for an exam in 3 hours.

    our prof got this formula, but it isnt working for the numbers?

    E = KQ / (a(a + l))

    where K is columbs constant,
    l = .119m
    a = .462418m
    Q = .0000177
  2. jcsd
  3. Feb 8, 2013 #2


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    2017 Award

    Staff: Mentor

    Re: uniformly charged rod(exam in 3 hours, plz help)

    What do you get, what do you expect?
    Maybe a is the distance to the closest point of the rod in this formula?

    You can calculate the electric field with an integral, this does not need any special formulas.

    I did some quick calculation and got $$E=KQ\frac{l}{a^2-\frac{l^2}{4}}$$
    up to constant prefactors, and with the assumption that the electric field is calculated outside the rod.
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