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Electric field, direction and magnitude

  1. Jun 24, 2010 #1
    1. The problem statement, all variables and given/known data

    A rod 14.0 cm long is uniformly charged and has a total charge of -22.0μC. Determine
    (a) the magnitude and
    (b) direction of the electric field along the axis of the rod at a point 36.0 cm from its centre.

    [I can do (b)]

    2. Relevant equations

    Electric field at the point due to a small element, ΔE=(k Δq)/(x^2)

    3. The attempt at a solution
    I got down to the total field at P being,
    (kQ/l) * integral of 1/x^2 from x=0.29 and x=0.43

    and I get 6.17 * 10^5 NC^-1

    But the answer says 1.59 * 10^6 NC^-1

    Are the answers wrong?
     
  2. jcsd
  3. Jun 24, 2010 #2

    ehild

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    The given answer is right, how did you get that wrong value?

    ehild
     
  4. Jun 24, 2010 #3
    (kQ/l) * integral of 1/x^2 from x=0.29 and x=0.43

    = 8.9876* 10^9 * -22 * 10^-6 / 0.14 ... etc
     
  5. Jun 24, 2010 #4

    ehild

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    And what is in place of etc?

    ehild
     
  6. Jun 24, 2010 #5
    I don't think you have considered the direction of E.
    E is a vector, and you need to treat the two components separately.
    Check any book for the field due to a wire, and you'll understand what you've missed.
     
  7. Jun 25, 2010 #6

    ehild

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    It depends what is meant on "axis of the rod". It should be the straight line along the rod.

    ehild
     
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