Two identical charged particles each having a mass $10 \,g$ and charge $2.0 \times 10^{-7}\,C$ area placed on a horizontal table with a separation of $L$ between then such that they stay in limited equilibrium. If the coefficient of friction between each particle and the table is $0.25$, find the value of $L$.[Use $g =10\,ms ^{-2}$ ]..........$cm$

Two spherical, nonconducting, and very thin shells of uniformly distributed positive charge $Q$ and radius d are located a distance $10d$ from each other. A positive point charge $q$ is placed inside one of the shells at a distance $d/2$ from the center, on the line connecting the centers of the two shells, as shown in the figure. What is the net force on the charge $q $ ?

Two free point charges $+q$ and $+4q$ are a distance $R$ apart. $A$ third charge is so  placed that the entire system is in equilibrium. Then the third charge is :-

When the distance between the charged particles is halved, the force between them becomes

When air is replaced by a dielectric medium of constant $k$, the maximum force of attraction between two charges separated by a distance

Two charges $ + 4e$ and $ + e$ are at a distance $x$ apart. At what distance, a charge $q$ must be placed from charge $ + e$ so that it is in equilibrium