The law, governing the force between electric charges is known as

The electric field between the two spheres of a charged spherical condenser

Two positive point charges of unequal magnitude are placed at a certain distance apart. A small positive test charge is placed at null point, then

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 ...........

An electron is moving round the nucleus of a hydrogen atom in a circular orbit of radius $r$. The coulomb force $\overrightarrow F $ between the two is (Where $K = \frac{1}{{4\pi {\varepsilon _0}}}$)

Two pith balls carrying equal charges are suspended from a common point by strings of equal length, the equilibrium separation between them is $r.$ Now the strings are rigidly clamped at half the height. The equilibrium separation between the balls now become