As shown in the figure, charges $ + q$ and $ – q$ are placed at the vertices $B$ and $C$ of an isosceles triangle. The potential at the vertex $A$ is

A table tennis ball which has been covered with conducting paint is suspended by a silk thread so that it hang between two plates, out of which one is earthed and other is connected to a high voltage generator. This ball

A hollow metallic sphere of radius $10 \;cm$ is charged such that potential of its surface is $80\; V$. The potential at the centre of the sphere would be

A charge $ + q$ is fixed at each of the points $x = {x_0},\,x = 3{x_0},\,x = 5{x_0}$….. $\infty$, on the $x – $axis and a charge $ – q$ is fixed at each of the points $x = 2{x_0},\,x = 4{x_0},x = 6{x_0}$,….. $\infty$. Here ${x_0}$ is a positive constant. Take the electric potential at a point due to a charge $Q$ at a distance $r$ from it to be $Q/(4\pi {\varepsilon _0}r)$. Then, the potential at the origin due to the above system of charges is

A thin spherical conducting shell of radius $R$ has a charge $q$. Another charge $Q$ is placed at the centre of the shell. The electrostatic potential at a point $p$ at distance $\frac{R}{2}$ from the centre of the shell is