Charges $+q$ and $-q$ are placed at points $A$ and $B$ respectively,which are a distance $2L$ apart. $C$ is the midpoint between $A$ and $B$. The work done in moving a charge $+Q$ along the semicircle $CRD$ is

If a charge is shifted from a low potential region to a high potential region,the electric potential energy

Consider a fixed uniformly charged insulating sphere with radius $R$ and total charge $+Q$. $A$ point charge $-q$ $(q \ll Q)$ with mass $m$ is released from rest at a distance of $3R$ from the centre of the charged sphere. When the point charge reaches the surface of the sphere, its speed is:
($\epsilon_0$ is the permittivity of vacuum, neglect gravitational forces).

Electron volt is a unit of

$A$ small sphere of radius $r_{1}$ and charge $q_{1}$ is enclosed by a spherical shell of radius $r_{2}$ and charge $q_{2}$. Show that if $q_{1}$ is positive,charge will necessarily flow from the sphere to the shell (when the two are connected by a wire) no matter what the charge $q_{2}$ on the shell is.

$125$ identical charged small spheres coalesce to form a big charged sphere. If the electric potential on each small sphere is $60 \text{ mV}$, then the electric potential on the bigger sphere formed is: (in $\text{ V}$)