Two point charges of $1 \, \mu\text{C}$ and $5 \, \mu\text{C}$ are placed at a distance of $4 \, \text{cm}$ apart. The ratio of the forces exerted by them on each other will be:

Two small spherical balls each carrying a charge $Q = 10\,\mu C$ are suspended by two insulating threads of equal lengths $L = 3\, m$ each,from a point fixed in the ceiling. It is found that in equilibrium,the threads are separated by an angle of $120^{\circ}$ between them,as shown in the figure. What is the tension in the threads? (Given: $\frac{1}{4\pi\varepsilon_0} = 9 \times 10^9\, N\cdot m^2/C^2$)

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

$A$ charge $Q$ is to be divided between two objects. The values of the charges on the objects so that the electrostatic force between them will be maximum is

Two charges $2 C$ and $6 C$ are separated by a finite distance. If a charge of $-4 C$ is added to each of them, the initial force of $12 \times 10^3 \,N$ will change to

Two point charges $+6 \mu C$ and $+10 \mu C$ kept at a certain distance repel each other with a force of $30 \ N$. If each charge is given an additional charge of $-8 \mu C$,the two charges: