$729$ small identical spheres each charged to an electric potential $3 \ V$ combine to form a bigger sphere. The electric potential of the bigger sphere is (in $V$)

Two charges $q_1$ and $q_2$ are separated by a distance of $30\ cm$. $A$ third charge $q_3$,initially at $C$ as shown in the figure,is moved along the circular path of radius $40\ cm$ from $C$ to $D$. If the difference in potential energy due to the movement of $q_3$ from $C$ to $D$ is given by $\frac{q_3 K}{4 \pi \epsilon_0}$,find the value of $K$.

Write an equation for the electric potential due to a system of charges.

Which one of the following is not a measurable quantity?

The electric potential $V$ of a charged spherical shell depends on the distance $r$ from its center. Which of the following graphs represents this dependence?

When a proton is accelerated through a potential difference of $1 \, V$, its kinetic energy is .......... $eV$.