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Homework Help: Electric field between two charges in 1D

  1. Feb 22, 2010 #1
    1. The problem statement, all variables and given/known data

    Two identical positive charges of +Q are 1 m apart. What is the magnitude and direction of the electric field at point A, 0.25 m to the right of the left-hand charge?

    2. Relevant equations

    E = kQ/r^2

    3. The attempt at a solution

    I summed up kQ+/(.25^2) and kQ+/(.75^2) and what I got was one of the answer choices, but apparently it was wrong. Evidently you have to subtract the .75 charge from the .25 to get the right answer. I also am unsure of which direction the electric field points.
     
  2. jcsd
  3. Feb 22, 2010 #2
    okay tekee, imagine that the point of interest is a positive charge. Which should be the default. A positive charge to the righthand side of it pushes it left. and a positive charge to the lefthand side of it will push right. So you will have to make appropriate changes to your answer due to that.
     
  4. Feb 22, 2010 #3
    point A is between the charges. The direction of the electric field is the direction of the force on a positive test-charge.
    What is the magnitude and direction of the field due to the positive charge 0.25 m to the left of A?
    What is the magnitude and direction of the field due to the positive charge 0.75 m to the right of A?
    Now you can add those fields like vectors.
     
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