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# electric field qn dont understand?? watch

1. this is the qn with the correct answer
what i dont understand is why do they minus for the electric field from both the POSITIVE charges to make it 0??? its TWO POSITIVE charges so shouldnt u add them up since minus is only for One positive and One negative charge????

also explain why the answer to the next part of the qn is 0: A charge of +4.5 μC is placed at point P.
State the magnitude of the force acting on this charge.
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2. (Original post by lolatmylifeee)
this is the qn with the correct answer
what i dont understand is why do they minus for the electric field from both the POSITIVE charges to make it 0??? its TWO POSITIVE charges so shouldnt u add them up since minus is only for One positive and One negative charge????

also explain why the answer to the next part of the qn is 0: A charge of +4.5 μC is placed at point P.
State the magnitude of the force acting on this charge.
You need to take into account the direction of the field from each point charge. Since both are positive, both are radial fields coming out from the point charges. At a point in between the charges, the fields will act in opposite direction, both away from their sources. You have to add (or subtract) fields like vectors.

For the second question, do you know an equation relating electric field strength, charge and force? (or just think of the definition of electric field strength). If E=0 at point P, then will there be any resultant force on the charge?

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