Yahoo Answers: Answers and Comments for Simple electric field question? [Physics]
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From Anonymous
enUS
Thu, 19 Sep 2019 14:59:10 +0000
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Yahoo Answers: Answers and Comments for Simple electric field question? [Physics]
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https://answers.yahoo.com/question/index?qid=20190919145910AAXAM7V
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From oldschool: We know the field won't be zero outside th...
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https://answers.yahoo.com/question/index?qid=20190919145910AAXAM7V
Thu, 19 Sep 2019 18:16:44 +0000
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/(1r)²
2.5(1r)² = 7.5r²
Take square roots of both sides
√2.5(1r) =+/ √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

From hoarseman: The field from A points towards B , and the (s...
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https://answers.yahoo.com/question/index?qid=20190919145910AAXAM7V
Thu, 19 Sep 2019 15:16:32 +0000
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) / (1D)