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Homework Help: Why is the resultant electric field pointed like this?

  1. Jun 9, 2012 #1
    Heres the question:

    Two charges (one is +4μC, the other is -8μC). They lie on 80mm apart, so you can imagine that the +4μC charge is on the left and the -8μC is on the right. Point P is equidistant from the two charges, draw two arrows at P to represent the directions and relative magnitudes of the component of the electric field at P due to each of the charges. Hence draw an arow labelled R at P to represent the resultant electric field at P.

    The main query I have is the resultant force bit of the question. Why is that the resultant force isn't just pointed horizontal towards the -8μC charge?

    It says in the mark scheme that, ''If the two charges were equal in magnitude but opposite in sign the resultant electric field at P would be directed horizontally to the right. Since one charge is twice the other, the resultant is directed slightly upwards and towards the right.''

    Why does the fact that the magnitude of one of the electric field is twice that of the other, cause the resultant to be altered from what 'should' be a straight-forward horizontal direction from charge +4μC to charge -8μC?
  2. jcsd
  3. Jun 9, 2012 #2


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    It sounds like the point P doesn't lie on the line connecting the two charges.
  4. Jun 9, 2012 #3
    If thats the case, then it makes sense having point P lying below both those charges.
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