In two cases, two identical conducting spheres are given equal charges, in one case of the same type whereas in another case of the opposite type. The distance between the spheres is not large as compared with the diameter. Let$F_1$ and $F_2$ be the magnitude of the force of interaction between the spheres, as shown, then

 

 

Two similar balloons filled with helium gas are tied to strings each of length $L.$ A body of mass $m$is tied to another end of the strings. The balloons float on air at distance $r.$ If the amount of charge on the balloons is same then the magnitude of charge on each balloon will be

Two identical small balls each have a mass $m$and charge $q.$ When placed in a hemispherical bowl of radius $R$with frictionless, nonconductive walls, the beads move, and at equilibrium the line joining the balls is horizontal and the distance between them is $R$(see figure). Neglect any induced charge on the hemispherical bowl. Then the charge on each bead is

$\left(\text{ here k}=\frac{1}{4\pi {\epsilon }_0}\right)$

A thin semi-circular ring of radius $r$ has a positive charge $q$ distributed uniformly over it. The net field $E$ at the centre $O$ is