Two point charges $q_1$ and $q_2$ are $l$ distance apart. If one of the charges is doubled and the distance between them is halved,the magnitude of force becomes $n$ times,where $n$ is

Two charges each equal to $2\,\mu C$ are $0.5\,m$ apart. If both of them exist inside vacuum,then the force between them is.......$N$

$ABC$ is a right-angled triangle in which $AB = 3\,cm$ and $BC = 4\,cm$. And $\angle ABC = \pi / 2$. The three charges $+15\,e.s.u.$,$+12\,e.s.u.$,and $-20\,e.s.u.$ are placed respectively on $A$,$B$,and $C$. The force acting on $B$ is.......$dynes$.

Two identical charges repel each other with a force equal to $10 \text{ mg}$ wt when they are $0.6 \text{ m}$ apart in air $(g = 10 \text{ ms}^{-2})$. The value of each charge is:

$A$ force $F$ acts between sodium and chlorine ions of salt (sodium chloride) when placed $1 \ cm$ apart in air. The permittivity of air is $\varepsilon_0$ and the dielectric constant of water is $K$. When a piece of salt is placed in water,the electrical force acting between sodium and chlorine ions $1 \ cm$ apart is:

Two identical simple pendulums each of length $L = 5 \, cm$ are suspended from the same support. When the bobs are given an equal charge of $q = 2 \, \mu C$ each, the distance between the bobs becomes $d = 6 \, cm$. Find the mass $m$ of each bob. (Take $g = 10 \, m/s^2$ and $k = 9 \times 10^9 \, N \cdot m^2/C^2$). (in $ \, kg$)