Electric field point charges

  • Thread starter tuggler
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  • #1
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Homework Statement



Two points are resting on a string. The first point is resting at x = 6.0 m and has charge q1 =−7.1 µC. The second point is resting at x = −4.0 m and has charge q2 = −4.3 µC.
At what location is the total electric field zero from the two points(other than infinity)?


Homework Equations



[tex]E =\frac{KQ}{r^2}[/tex]

[tex]\frac{q_1}{r_1^2} = \frac{q_2}{r_2^2}[/tex]



The Attempt at a Solution



I divided away the constant K from my second equation because they cancel out when you set them equal to each other.

I don't know what my [tex]r_1,r_2[/tex] should be here?
 

Answers and Replies

  • #2
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Why don't you set the distance from the first charge x and define the distance from the other with x and the distance between the two charges? Thus you introduce only one variable in one equation.
 
  • #3
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Don't forget that the contribution to the electric field from each charge has direction, so, if the point is between the two charges, the contribution from the charge at x = 6 is pointing in the negative x-direction, and the contribution from the charge at x = -4 is pointing in the positive x-direction.
 
  • #4
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I am not following can you guys elaborate more please?
 

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