Two point charges $Q$ and $-3 Q$ are placed at some distance apart. If the electric field due to $-3 Q$ at the location of $Q$ is $E \hat{i}$,then the electric field due to $Q$ at the location of $-3 Q$ is:

The point charges $+q, -q, -q, +q, +Q$ and $-q$ are placed at the vertices of a regular hexagon $ABCDEF$ as shown in the figure. The electric field at the centre of the hexagon '$O$' due to the five charges at $A, B, C, D$ and $F$ is twice the electric field at centre '$O$' due to charge $+Q$ at $E$ alone. The value of $Q$ is

Consider a circular loop that is uniformly charged and has a radius $R = a \sqrt{2}$. Find the position along the positive $z$-axis of the Cartesian coordinate system where the electric field is maximum,assuming the ring is placed in the $xy$-plane at the origin.

$A$ charged water drop of radius $0.1 \, \mu m$ is in equilibrium under an electric field. The charge on the drop is equivalent to the electronic charge. The intensity of the electric field is ........ $N/C$.

Two infinite planes, each with a uniform surface charge density $+\sigma$, are kept such that the angle between them is $30^{\circ}$. The electric field in the region between them is given by:

The insulation property of air breaks down at $E = 3 \times 10^6 \ V/m$. The maximum charge that can be given to a sphere of diameter $5 \ m$ is approximately (in coulombs):