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

Two point charges $q_{ A }=3\; \mu \,C$ and $q_{ B }=-3\; \mu \,C$ are located $20\; cm$ apart in vacuum.

$(a)$ What is the electric field at the midpoint $O$ of the line $AB$ joining the two charges?

$(b)$ If a negative test charge of magnitude $1.5 \times 10^{-9}\; C$ is placed at this point, what is the force experienced by the test charge?

An oil drop carries six electronic charges, has a mass of $1.6 \times 10^{-12} g$ and falls with a terminal velocity in air. The magnitude of vertical electrical electric field required to  make the drop move upward with the same speed as was formely moving is ........$kN/C$

Electric field strength due to a point charge of $5\,\mu C$ at a distance of $80\, cm$ from the charge is

What is called electric field ?

The intensity of the electric field required to keep a water drop of radius ${10^{ - 5}}\, cm$ just suspended in air when charged with one electron is approximately