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Where would you place a proton to produce this field at the origin?

  1. Aug 26, 2008 #1
    1. The problem statement, all variables and given/known data

    You want to create an electric field = < 0, 5e4,0 > N/C at location < 0, 0, 0>.
    Where would you place a proton to produce this field at the origin?

    2. Relevant equations

    [tex]\vec E = q\hat{r} / 4\pi\varepsilon r^2[/tex]

    3. The attempt at a solution

    I'm not sure how to treat [tex]\hat{r}[/tex] in the equation. Obviously, I know it's equal to r/rmag, but rmag is what's throwing me.
     
  2. jcsd
  3. Aug 26, 2008 #2

    LowlyPion

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    An electric field is a vector field. So where you place the proton will determine both the magnitude and the direction of the electric field.
     
  4. Aug 26, 2008 #3

    Doc Al

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    That's just a unit vector (magnitude = 1) giving the direction of the field. The field from a positive charge is radially outward.
     
  5. Aug 26, 2008 #4
    Ok, I thought that unit vector might be 1, so I solve for [tex]r^2[/tex], correct? I tried that and didn't get the right answer.
     
  6. Aug 26, 2008 #5

    LowlyPion

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    What values did you use?
     
  7. Aug 26, 2008 #6
    5e4 = [(1.6e-19)(9e9)] / r^2

    I got r = 1.69707e-7
     
  8. Aug 26, 2008 #7

    LowlyPion

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    Why do you think this is incorrect?
     
  9. Aug 26, 2008 #8
    Because when I submit it online it tells me that's the wrong answer. I'm not sure what I'm doing wrong.
     
  10. Aug 26, 2008 #9

    LowlyPion

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    Is it possible it's your coordinates for placing the proton? They are asking you where you would place the proton to affect this electric field vector at 0,0,0.
     
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