Electrostatic force between two identical charges placed in vacuum at distance of $$r$$ is F. A slab of width $$\frac{r}{5}$$ and dielectric constant 9 is inserted between these two charges, then the force between the charges is

An electric dipole with dipole moment $$5 \times 10^{-7} \mathrm{C}-\mathrm{m}$$ is in the electric field of $$2 \times 10^4 \mathrm{NC}^{-1}$$ at an angle of $$60^{\circ}$$ with the direction of the electric field. The torque acting on the dipole is

Two positive point charges of $$10 \mu \mathrm{C}$$ and $$12 \mu \mathrm{C}$$ are placed 10 cm apart in air. The work done to bring them 6 cm closer is

Two charges $$10 ~\mu \mathrm{C}$$ and $$-10 ~\mu \mathrm{C}$$ are placed at points $$A$$ and $$B$$ separated by a distance of $$10 \mathrm{~cm}$$. Find the electric field at a point $$P$$ on the perpendicular bisector of $$A B$$, at a distance of $$12 \mathrm{~cm}$$ from its mid-point.