Electrostatics Question 185

Question: Two similar spheres having $ +q $ and $ -q $ charge are kept at a certain distance. $ F $ force acts between the two. If in the middle of two spheres, another similar sphere having $ +q $ charge is kept, then it experience a force in magnitude and direction as [MP PET 1996]

Options:

A) Zero having no direction

B) $ 8F $ towards $ +q $ charge

C) $ 8F $ towards $ -q $ charge

D) $ 4F $ towards $ +q $ charge

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Answer:

Correct Answer: C

Solution:

Initially, force between A and C

$ F=k\frac{Q^{2}}{r^{2}} $

When a similar sphere B having charge +Q is kept at the mid point of line joining A and C, then Net force on B is $ F _{net}=F _{A}+F _{C} $

$ =k\frac{Q^{2}}{{{( {r}/{2}; )}^{2}}}+\frac{kQ^{2}}{{{( {r}/{2}; )}^{2}}}=8\frac{kQ^{2}}{r^{2}}=8F $ .



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