1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Very simple charge question, please review

  1. Jul 14, 2010 #1


    User Avatar

    1. The problem statement, all variables and given/known data
    A -14.1 nC charge is located at position (x,y) = (2.48 cm, 1.24 cm). At what (x,y) position is the electric field -262600.0i? (Enter your x position first followed by the y position.)

    2. Relevant equations
    E = kQ/r2
    E = electric field strength
    k = 9 x 109
    r = distance to the point from the charge

    3. The attempt at a solution

    E = kQ/r2
    ∴ r = √(kQ/E)
    r = 0.02198

    original position: (0.0248m, 0.0124m)
    electric field: -262600.0i,
    unit vector 'i' indicates only x component, no y component:
    therefore y component is the same (electric field vectors go straight in toward -'ve charge)

    therefore x-component is..
    0.0248 + r
    =0.0248 + 0.02198
    = 0.04678m

    final answer:
    (0.04678m, 0.0124m)

    Originally what I did was
    0.0248 - r
    =0.0248 - 0.02198
    = 2.82E-3

    final answer:
    (2.82E-3m, 0.02198m)

    the computer rejected this.

    The computer only accepted (0.04678m, 0.0124m) as the correct answer

    I was wondering... is the other answer equally as valid or am I missing something?
  2. jcsd
  3. Jul 15, 2010 #2
    For the other answer, E would be +262600.0i and not -262600.0i.

    You could draw the field lines around the charge and see for yourself.
  4. Jul 15, 2010 #3


    User Avatar

Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook