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

$n$ small drops of same size are charged to $V$ $volts$ each. If they coalesce to form a signal large drop, then its potential will be

A charge $q$ is placed at $O$ in the cavity in a spherical uncharge $d$ conductor. Point $S$ is outside the conductor. If the charge is displaced from $O$ towards $S$ still remaining with in the cavity,

Two charges $+q$ and $-3q$ are placed on $x-$ axis separated by a distance $d$. ($-3q$ is right of $q$) Where should a third charge $2q$ be placed such that it will not experience any force ?

Four charges are placed at the circumference of a dial clock as shown in figure. If the clock has only hour hand, then the resultant force on a charge $q_0$ placed at the centre, points in the direction which shows the time as