If two charges of $1$ coulomb each are placed $1 \,km$ apart, then the force between them will be ……….. $N$

Two positive charges of $20$ $coulomb$ and $Q\;coulomb$ are situated at a distance of $60\,cm$. The neutral point between them is at a distance of $20\,cm$ from the $20\,coulomb$ charge. Charge $Q$ is…..$C$

Three identical charged balls each of charge $2 \,C$ are suspended from a common point $P$ by silk threads of $2 \,m$ each (as shown in figure). They form an equilateral triangle of side $1 \,m$.

The ratio of net force on a charged ball to the force between any two charged balls will be ………..

Two identical spheres each of radius $R$ are kept at center-to-center spacing $4R$ as shown in the figure. They are charged and the electrostatic force of interaction between them is first calculated assuming them point like charges at their centers and the force is also measured experimentally. The calculated and measured forces are denoted by $F_c$ and $F_m$ respectively.
($F_c$ and $F_m$ denote magnitude of force)

Two small conducting spheres of equal radius have charges $ + 10\,\mu C$ and $ – 20\,\mu C$ respectively and placed at a distance $R$ from each other experience force ${F_1}$. If they are brought in contact and separated to the same distance, they experience force ${F_2}$. The ratio of ${F_1}$ to ${F_2}$ is