Two charges placed in air repel each other by a force of ${10^{ - 4}}\,N$. When oil is introduced between the charges, the force becomes $2.5 \times {10^{ - 5}}\,N$. The dielectric constant of oil is

Two identical conducting spheres with negligible volume have $2.1\, nC$ and $-0.1\, nC$ charges, respectively. They are brought into contact and then separated by a distance of $0.5 \,m$. The electrostatic force acting between the spheres is $.......... \, \times 10^{-9} \,N$

[Given : $4 \pi \varepsilon_{0}=\frac{1}{9 \times 10^{9}} SI$ unit]

The diagrams depict four different charge distributions. All the charged particles are at same distance from origin $(i.e. OA = OB = OC = OD)$ $F_1$ , $F_2$ , $F_3$ and $F_4$ are the magnitude of electrostatic force experienced by a point charge $q_0$ kept at origin in figure $-1$ , figure $-2$ , figure $-3$ and figure $-4$ respectively. Choose the correct statement.

Two equal charges of magnitude $Q$ each are placed at a distance $d$ apart. Their electrostatic energy is $E$. A third charge $-Q / 2$ is brought midway between these two charges. The electrostatic energy of the system is now

Electric charges of $1\,\mu C,\, - 1\,\mu C$ and $2\,\mu C$ are placed in air at the corners $A$, $B$ and $C$ respectively of an equilateral triangle $ABC$ having length of each side $10 \,cm$. The resultant force on the charge at $C$ is......$N$

A given charge is situated at a certain distance from an electric dipole in the end-on position experiences a force $F$. If the distance of the charge is doubled, the force acting on the charge will be