The surface charge density of a conductor is $12\times {10}^{-12} {\mathrm{cm}}^{-2}$. If the conductor is surrounded by a medium of dielectric constant $3.14$, the magnitude of electric field just outside the conductor is $\left(\frac{1}{4\pi {\epsilon }_0}=9\times {10}^9 {\text{N m}}^2 {\mathrm{C}}^{-2}\right)$

Two spheres $A$ and $B$ are having radii $5 \mathrm{cm} \text{and} 10 \mathrm{cm}$ and carrying charges of $+5 \mathrm{C} \text{and}+15 \mathrm{C}$, respectively, distributed uniformly. Their centres are separated by $80 \mathrm{cm}$. The electric field on the line joining the centres of the spheres will be zero at a distance from the centre of $A$ equal to

The surface density of charge on the surface of a charged conductor in air is $0.885 \mathrm{\mu C} {\mathrm{m}}^{-2}$. If ${\epsilon }_0=8.85\times {10}^{-12} {\mathrm{C}}^2 {\mathrm{N}}^{-1} {\mathrm{m}}^{-2}$ then the outward force per unit area of the charged conductor is

A metallic solid sphere is placed in a uniform electric field. The lines of force follow the path(s) shown in figure as

$4 \times 10^{10}$ electrons are removed from a neutral metal sphere of diameter $20 \mathrm{cm}$ placed in air. The magnitude of the electric field (in $\mathrm{N} {\mathrm{C}}^{-1}$ ) at a distance of $20 \mathrm{cm}$ from its centre is

A spherical conductor of radius $2 \mathrm{cm}$ is uniformly charged with $3 \mathrm{nC}$. What is the electric field at a distance of $3 \mathrm{cm}$ from the centre of the sphere? 

The magnitude of point charge due to which the electric field $30 \mathrm{cm}$ away has a magnitude of $2 \mathrm{N} {\mathrm{C}}^{-1}$ will be,

Electric field intensity at points in between and outside two thin separated parallel sheets of infinite dimensions with like charges of same surface charge density ($\sigma$) are ____ and ____, respectively.

An electron falls from rest through a vertical distance $h$ in a uniform and vertically upward directed electric field $E$. The direction of electric field is now reversed, keeping its magnitude the same. A proton is allowed to fall from rest in it through the same vertical distance $h$. The time of fall of the electron, in comparison to the time of fall of the proton is