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Homework Help: Electric fields of particles

  1. Feb 3, 2012 #1
    1. The problem statement, all variables and given/known data
    You want to create an electric field = < 0, 3x10^4,0 > N/C at location < 0, 0, 0>.
    Where would you place a proton to produce this field at the origin?

    2. Relevant equations
    1/4?? * q/r^2 = 3x10^4 N/C

    (if you can't see the 1/4th part of the equation it's 1/(4(pi)(epsilon-not)) == 9.0x10^9 or just k)
    3. The attempt at a solution
    I moved everything over so that I can solve for r^2 and got this as my equation:
    r = sqrt((9.0x10^9)(1.6x10^-19)/(3x10^4))

    I ended up getting 2.19x10^-7 however its' saying it's not correct. I have it set up as a vector:
    <0, 2.19x10^-7, 0>

    Does it need to be negative for a proton in relation to the electric field?
     
    Last edited: Feb 3, 2012
  2. jcsd
  3. Feb 3, 2012 #2
    if you place a proton at 2.19E-7 above the x-axis, which way will a +1C charge accelerate when it is placed at the origin?
     
  4. Feb 3, 2012 #3
    I have nooo idea. I'm kind of hazy as to the magnitude and direction of charged particles, so I'm not sure if its pointing up or down
     
  5. Feb 3, 2012 #4
    like charges (attract or repel) each other
     
  6. Feb 3, 2012 #5
    Oh wait, if it's at the origin, a proton would move away, so the sign would be negative, wouldn't it?
     
  7. Feb 3, 2012 #6
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