The surface charge density of a thin charged disc of radius $R$ is $\sigma $. The value of the electric field at the centre of the disc is $\frac{\sigma }{{2\,{ \in _0}}}$. With respect to the field at the centre, the electric field along the axis at a distance $R$ from the centre of the disc

Three charged particle $A, B$ and $C$ with charges $-4 q,  2 q$ and $-2 q$ are present on the circumference of a circle of radius $d$. the charged particles $A, C$ and centre $O$ of the circle formed an equilateral triangle as shown in figure. Electric field at $O$ along $x-$direction is

A positively charged ball hangs from a silk thread. We put a positive test charge ${q_0}$ at a point and measure $F/{q_0}$, then it can be predicted that the electric field strength $E$

The maximum value of electric field on the axis of a charged ring having charge $Q$ and radius $R$ is

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 total charge $q$ is divided as $q_1$ and $q_2$ which are kept at two of the vertices of an equilateral triangle of side a. The magnitude of the electric field $E$ at the third vertex of the triangle is to be depicted schematically as a function of $x=q_1 / q$. Choose the correct figure.