When two identical point charges are placed at a distance of $5 \, cm$, they experience a repulsive force of $0.144 \, N$. The value of each charge in microcoulombs $(\mu C)$ is:

Two equally charged small balls placed at a fixed distance experience a force $F$. $A$ similar uncharged ball after touching one of them is placed at the middle point between the two balls. The force experienced by this ball is:

Two electric charges $+q$ and $+q$ are placed at a distance $r$. The force between them is $F$. If one charge is fixed and the other moves in a circle of radius $r$,the work done will be .......

Write the general equation for the Coulombian force on a charge ${q_1}$ due to a system of charges ${q_1}, {q_2}, \dots, {q_n}$.

Two point charges $A$ and $B$ with magnitudes $+4q$ and $-4q$ are placed along a line separated by a distance $r$. The force acting between them is $F$. If $25\%$ of the charge from point $A$ is transferred to point $B$,the force between the charges now becomes:

Two free positive charges $4q$ and $q$ are at a distance $l$ apart. What charge $Q$ is needed to achieve equilibrium for the entire system and where should it be placed from charge $q$?