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Homework Help: Electric Potential and Charges Problem

  1. May 11, 2010 #1
    1. The problem statement, all variables and given/known data

    Point P is at the origin. Charge A is at (-3,0) and Charge B is at (4,0). What is the electric potential at point P. Lets assume they are both positive charges for now, but I am interested to know if and how it changes if either/both of the charges are negative.

    2. Relevant equations

    I assume I will need to use V=kq/r but I could be mistaken.

    3. The attempt at a solution

    Once I get both the potentials using V=kq/r can I simply add them together to get the potential at P? If one charge was negative do I subtract the potential from that one from the positive charge to get the potential at P?

    Thank you
  2. jcsd
  3. May 11, 2010 #2
    Yes, you can use Kq/r to calculate the potential due to each charge at P. The great thing about using potentials is that it is a scalar and you can just add them. If you were using the E-field you would have to add the vectors which is more difficult. If charge is negative then it makes the potential negative since v = kq/r, so if q is negative then v will be negative as well.
  4. May 11, 2010 #3
    Thank you very much for the quick help. I thought I was on the right track but wanted to get some expert help :D.

    Thanks again
  5. May 11, 2010 #4


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    Science Advisor
    Homework Helper

    Hi buyerat! :wink:
    Yup! … potentials add just like numbers. :smile:
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