Question

Two equally charged, indentical metal spheres `A` and `B` repel each other with a force `F"`. The spheres are kept fixed with a distance `r` between them. A third identical, but uncharged sphere `C` is brought in contact with `A` and The magnitude of the net electric force on `C` is
A. `F`
B. `3F//4`
C. `F//2`
D. `F//4`

Answer 1

Correct Answer - a
Initially

`F=k(Q^(2))/(r^(2))`….(i)
Finally

Force on `C` due to `A`, `F_(A)= (k(Q//2)^(2))/((r//2)^(2))=(KQ^(2))/(r^(2))`
Force on `C` due to `B`, `F_(B)=(KQ(Q//2))/((r//2)^(2))=(2KQ^(2))/(r^(2))` ltbegt `:.` Net force on `C`, `F_("net")= F_(B)-F_(A)= (KQ^(2))/(r^(2))=F`