Two equally charged identical metal spheres A and B repel each other with a force F. Another identical uncharged sphere C is touched to A and then placed midway between A and B. The net force on C is in the direction:
A
F towards A
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B
F towards B
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C
2F towards A
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D
2F towards B
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Solution
The correct option is AF towards A The spheres are equally charged. Let the charge be q. Now, using coulombs law, kq2/r2=F ( r is the distance between the two spheres ) When the uncharged sphere touches A, q/2 charge gets transferred to C Now, force on C, =k(q/2)(q/2)(r/2)2−k(q/2)(q)(r/2)2=kq2/r2−2kq2/r2=−F Net force is thus towards A.