If the electric potential of the inner sphere is $10\, V$ and that of the outer shell is $50\, V$,then the potential at the common centre is :- (in $, V$)

$A$ thin conducting spherical shell of radius $R$ has a charge $q$. Another charge $Q$ is placed at the center of the shell. The electrostatic potential at a point $P$ at a distance $R/2$ from the center of the shell is:

If four charges $q_1 = +1 \times 10^{-8} \text{ C}$, $q_2 = -2 \times 10^{-8} \text{ C}$, $q_3 = +3 \times 10^{-8} \text{ C}$, and $q_4 = +2 \times 10^{-8} \text{ C}$ are kept at the four corners of a square of side $1 \text{ m}$, then the electric potential at the centre of the square is: (in $\text{ V}$)

$A$ regular hexagon of side $9 \ cm$ has a charge $5 \mu C$ at each of its vertices. The electric potential at its centre is $..........V$. $(k = 9 \times 10^9 \ Nm^2 C^{-2})$

$A$ point charge $q$ is held at the centre of a circle of radius $r$. $B$ and $C$ are two points on the circumference of the circle,and $A$ is a point outside the circle. If $W_{AB}$ represents the work done by the electric field in taking a charge $q_0$ from $A$ to $B$,and $W_{AC}$ represents the work done from $A$ to $C$,then:

Two identical metal balls of radius $r$ are at a distance $a$ $(a \gg r)$ from each other and are charged,one with potential $V_1$ and other with potential $V_2$. The charges $q_1$ and $q_2$ on these balls in $CGS$ $esu$ are