Two identical conducting spheres P and S with charge Q on each, repel each other with a force 16N. A third identical uncharged conducting sphere R is successively brought in contact with the two spheres. The new force of repulsion between P and S is :
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Question

Two identical conducting spheres P and S with charge Q on each, repel each other with a force 16N. A third identical uncharged conducting sphere R is successively brought in contact with the two spheres. The new force of repulsion between P and S is :

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G1 Physics · Accepted Answer

Initially: Force ∝ Q² and the force is 16 N. When uncharged sphere R touches P: Charge on P = Q/2 Charge on R = Q/2 Then R touches S, which initially has charge Q. Total charge shared by R and S: Q/2 + Q = 3Q/2 Therefore each gets: 3Q/4 Final charges: P = Q/2 S = 3Q/4 New force: F' / F = [(Q/2)(3Q/4)]/Q² = 3/8 Therefore: F' = 16 × 3/8 = 6 N