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# simple electric field question?

### 2 Answers

- oldschoolLv 74 months agoFavorite Answer
We know the field won't be zero outside the charges because their fields are in the same direction left of the origin (both point 180° and right of (1,0) where both point at 0°. There fields oppose between the charges and that is where E = 0 at the point where the fields are equal and cancel. Let r be the distance right from the origin.

2.5/r² = 7.5/(1-r)²

2.5(1-r)² = 7.5r²

Take square roots of both sides

√2.5(1-r) =+/- √7.5r

√2.5 = √2.5r+√7.5r = r(√2.5 +√7.5)

r = √2.5/(√2.5 +√7.5) = 0.366 <<<<<<

Check the negative solution

r = √2.5/(√2.5 - √7.5) = -1.366 which can't be right because the fields add left of the origin. Discard solution r = -1.366

E = 0 at x = +0.366

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- hoarsemanLv 74 months ago
The field from A points towards B , and the (stronger) field from B ,points towards A. At some point between them, therefore there will be a point where their fields cancel out .

From the definition of E being proportional to Q/D, you get :

Q(a) / D = Q(b) / (1-D)

- hoarsemanLv 74 months agoReport
My apologies for accidently dropping the "square" of the distances

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