The bob of a simple pendulum has mass $2\,g$ and a charge of $5.0\,\mu C$. It is at rest in a uniform horizontal electric field of intensity $2000\,\frac{V}{m}$. At equilibrium, the angle that the pendulum makes with the vertical is (take $g = 10\,\frac{m}{{{s^2}}}$)

Two equal negative charges $-\, q$ each are fixed at the points $(0, a)$ and $(0, -a)$ on the $Y$ -axis. A positive charge $Q$ is released from rest at the point $(2a, 0)$ on the $X$ -axis. The charge $Q$ will :-

Charges $q$, $2q$, $3q$ and $4q$ are placed at the corners $A$,$ B$,$ C$ and $D$ of a square as shown in the following figure. The direction of electric field at the centre of the square is along

A thin semi-circular ring ofradius $r$ has a positive charge $q$ distributed uniformly over it. The net field $\vec E$ at the centre $O$ is

Two particles ${A}$ and ${B}$ having charges $20\, \mu {C}$ and $-5\, \mu {C}$ respectively are held fixed with a separation of $5\, {cm}$. At what position a third charged particle should be placed so that it does not experience a net electric force?