Charges $4Q$,$q$,and $Q$ are placed along the $x$-axis at positions $x = 0$,$x = l/2$,and $x = l$,respectively. Find the value of $q$ such that the net force on charge $Q$ is zero.

$A$ charge of $0.8 \text{ C}$ is divided into two charges $Q_{1}$ and $Q_{2}$. These are kept at a separation of $30 \text{ cm}$. The force on $Q_{1}$ is maximum when

Two particles of equal mass $m$ and equal charge $q$ are separated by a distance of $16 \text{ cm}$. They do not experience any net force. The value of $\frac{q}{m}$ is . . . . . . (where $G$ is the universal gravitational constant and $\epsilon_0$ is the permittivity of free space).

Consider the charges $q, q$,and $-q$ placed at the vertices of an equilateral triangle of side $l$,as shown in the figure. What is the force on each charge?

Two small spheres,each having an equal positive charge $Q$ (Coulomb),are suspended by two insulating strings of equal length $L$ (metre) from a rigid hook. The whole setup is taken into a satellite where there is no gravity. The two balls are now held by electrostatic forces in a horizontal position. The tension in each string is then:

$A$ charge $q_1$ exerts some force on a second charge $q_2$. If a third charge $q_3$ is brought near,the force of $q_1$ exerted on $q_2$: