A and B are two identical point sized metal spheres each holding the same charge .q.. These two are separated by certain distance and the mutual electrostatic force between them is F. If a third identical uncharged sphere .C. is touched with A and kept exactly at the midpoint of line joining A and B, what is the resulting force on C and its direction?

Explanation

Force between two charges

When third identical uncharged sphere touched with A and placed at the mid point of AB, then

`F_("net") = F_(1) - F_(2)`
`K ((q^(2)//4))/(r^(2)//4)- K ((q^(2)//2))/(r^(2)//4) = (Kq^(2))/(r^(2))-2.(Kq^(2))/(r^(2))= F- 2F`
`F_("net")= -F` i.e., resultant force is F towards A