Basic Electrostatics - Why Did I Get This Multiple Choice Question Wrong

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Basic Electrostatics - Why Did I Get This Multiple Choice Question Wrong

[From: ] [author: ] [Date: 13-01-21] [Hit: ]

in this case athe force equations and simple algebra instead of qualitative arguments.You invoked a qualitative argument that, it turned out, just wasnt valid.But you had no way of validating it.That is called wishful thinking.......

but clearly (it should be clear!!) if e = 100 and x = 1 then 5/(101)² - 3/1 is NEGATIVE.
So the force transitions from negative at relative distances close to Q1 and positive at longer and longer distances (that is 5/1001² - 3/1000² will be POSITIVE)
IOW as the relative separation between Q1 & Q2 decreases relative to the distance between A and both of them, the +5 charge comes to predominate.
-=-=
You really should prefer to use quantitative arguments, in this case athe force equations and simple algebra instead of qualitative arguments. You invoked a qualitative argument that, it turned out, just wasn't valid. But you had no way of validating it. That is called wishful thinking.

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Call the distance from -e to Q1, d1
Call the distance from -e to Q2, d2

If -e is very, very close to Q1, -e will be strongly repelled by Q1.
Q2 will have relatively little effect because d2 is very large compared to d1 (d1/d2 is very small).
So overall, the force on -e is large and to the left

If -e is very, very far to the left from Q1 (and therefore from Q2) ,then d1 and d2 are relatively similar d1/d2 = 1 approx. In this case, the dominant force is the attraction from the larger charge (Q2) and the force on -e is weak and to the right.

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