$n$ 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

Charge $q$ is uniformly distributed over a thin half ring of radius $R$. The electric field at the centre  of the ring is 

Two point charges of $ + 2\,\mu C$ and $ + 6\,\mu C$ repel each other with a force of $12\, N$. If each is given an additional charge of $ - 4\,\mu C$, then force will become

Two capacitors $C_1$ and $C_2 = 2\,C_1$ are connected in a circuit with a switch between them as shown in the figure. Initially the switch is open and $C_1$ holds charge $Q$. The switch is closed. At steady state, the charge on capacitors will be

Four charges equal to $-Q$ are placed at the four corners of a square and a charge $q$ is at its centre. If the system is in equilibrium, the value of $q$ is

Five balls marked a to $e$ are suspended using separate threads. Pairs $(b, c)$ and $(d, e)$ show electrostatic repulsion while pairs $(a, b),(c, e)$ and $(a, e)$ show electrostatic attraction. The ball marked a must be