Two equally charged metal spheres $A$ and $B$ repel each other with a force of $4\times {10}^{-5} \mathrm{N}$. Another identical uncharged sphere $C$ is touched to $A$ and then placed at the mid point of the line joining the spheres $A$ and $B$. The net electric force on the sphere $C$ is

A hollow conducting sphere is placed in an electric field produced by a point charge placed at $P$ as shown in figure. Let $V_A, V_B, V_C$ be the potentials at points $A, B$ and $C$, respectively. Then

A spherical conductor $A$ is placed concentrically inside a hollow spherical conductor $B$. The charge $+Q$ is given to $A$ and $B$ is earthed. Then the electric field is not zero