What will be the magnitude of electric field at point $O$ as shown in figure ? Each side of the figure is $I$ and perpendicular to each other.

The intensity of electric field required to balance a proton of mass $1.7 \times {10^{ – 27}} kg$ and charge $1.6 \times {10^{ – 19}} C$ is nearly

A ring of radius $R$ is charged uniformly with a charge $+\,Q$ . The electric field at a point on its axis at a distance $r$ from any point on the ring will be

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

Give physical meaning of electric field.