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Homework Help: Homework on quiz i took alredy

  1. Apr 9, 2010 #1
    1. The problem statement, all variables and given/known data

    Charges +Q and –Q are arranged at the corners of a square as shown. When the electric field and the electric potential V are determined at P, the center of the square, we find that

    2. Relevant equations

    -----------P----------- There is line crossging through P from top left +Q and to bottom right +Q and same for -Q's


    3. The attempt at a solution
    1. E = 0 and V > 0
    2. E ≠ 0 and V < 0
    3. E= 0 and V= 0
    4. E ≠ 0 and V > 0
    5. None of these is correct. 0%
    Last edited: Apr 9, 2010
  2. jcsd
  3. Apr 10, 2010 #2


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    Science Advisor
    Homework Helper
    Gold Member

    If you took this quiz already as you seem to imply in the title, what answer did you give and what was your reasoning?
    Last edited: Apr 10, 2010
  4. Apr 10, 2010 #3
    Question seems to be chopped off?
  5. Apr 10, 2010 #4
    i choose none of these are correct because none of them seemed correct to me. notic the 0% next to the last option(none of these are correct)

    the question is there in full. it was a multiple choise question.
  6. Apr 10, 2010 #5
    That isn't a reason. That is circular reasoning.
  7. Apr 10, 2010 #6


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    Staff: Mentor

    Let's start with the electric filed - how do you think, what is electric field in P?
  8. Apr 10, 2010 #7
    are the two fields canceled by the push and pull of the oppositely charged particles...leading to 0
  9. Apr 10, 2010 #8


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    Staff: Mentor

    Right. It is even easier if you think in terms of the definition - force acting on the unit charge. If you place any charge in point P is it pulled in two opposite directions - and these pulls cancel out, and it is pushed in two opposite directions - once agin, forces cancels out.

    What about potential?
  10. Apr 10, 2010 #9
    Since potential is a scalar, you can just add up the value and account for sign. I can see that for every positive charge at a fixed distance there is a corresponding negative charge. This is why when I add it up, the net potential is zero.

    So E=0 and V=0????
  11. Apr 10, 2010 #10
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