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Electric field?

  1. Sep 2, 2009 #1
    Electric field???

    1. The problem statement, all variables and given/known data

    A point charge of -4 uC is located at x = 2 m, y = -2 m (called A) . A second point charge of 12 uC is located at x = 1 m, y = 2 m. (called B)

    (a) Find the magnitude and direction of the electric field at x = -1 m, y = 0. (called C)

    (b) find the angle. I know i can find angle using arctan after i find the x and y components above. so this im not too worried about.




    2. Relevant equations

    Enet = Enetx + Enety

    kq / r^3 * R where R is the vector (equation given by TA)


    3. The attempt at a solution

    i started by finding the two vectors
    rAC = -3,2 magnitued is sqrt(13)
    rBC = -2,-2 magnitued is sqrt(8)
    then i jumped into Enet = EAC + EBC
    did kq / r^3 * R for point AC
    k(-4e-6)/((sqrt(13))^3) * <-3,2> this gives an x and a y
    then the same for BC
    k(12e-6)/((sqrt(8))^3) * <-2,-2> this gives an x and a y

    i added x components togeather then the y components and said that was by
    Enet vector. then just found the magnitued.
    my Enet vector was some crazy numbers of
    <-7241.832,-18323.896>
    that is not right lol
    and this is where im stuck
    any help would be great!!!
     
  2. jcsd
  3. Sep 2, 2009 #2

    tms

    User Avatar

    Re: Electric field???

    Check your arithmetic again, especially for the [tex]\vec j[/tex] component.
     
  4. Sep 2, 2009 #3
    Re: Electric field???

    Yeah, I did the problem, and your equations are correct (but I got a different answer!). You probably mistyped on your calculator, or added the components incorrectly.
     
    Last edited: Sep 2, 2009
  5. Sep 2, 2009 #4
    Re: Electric field???

    ok... here is what i did.
    first i started with k(-4e-6)/((sqrt(13))^3) * <-3,2> equation
    k = 9e9
    so 9e9*-4e-6 = -36000
    (sqrt(13)) ^ 3 = 46.8722
    so -36000/ 46.8722 = -768.04643
    then take that number and * by <-3,2> to get
    <2304.1393,-1536.09285> <x,y> respectivly
    do the same thing for k(12e-6)/((sqrt(8))^3) * <-2,-2>
    9e9 * 12e-6 = 108000
    (sqrt(8))^3 = 22.6274
    so 108000/22.6274 = 4772.970773
    then * <-2,-2> to get
    <-9545.94155,-9545.94155> <x,y> respectivly
    at the two x and the two y's and i get the same answer as posted??

    can you guys see where i went wrong?
    might be using the wrong k value?
    let me know
    thanks

    well... i do get a different J component and it is -11082.0344 not what i had in the original post but my I component i get the same.
    is this right??
     
  6. Sep 2, 2009 #5
    Re: Electric field???

    never mind...
    i got it

    thanks everyone for the help!!!!
    just a stupid plug-in error lol
     
  7. Sep 3, 2009 #6
    Re: Electric field???

    1.a Cos a = 4/*65, E1 = 12/13k, E2 = 4/5k, use cos function theorem to find electric field!
     
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