Four point charges $q_{A}=2\; \mu C, q_{B}=-5\; \mu C, q_{C}=2\; \mu C,$ and $q_{D}=-5\; \mu C$ are located at the corners of a square $ABCD$ of side $10\; cm$. What is the force on a charge of $1\; \mu C$ placed at the centre of the square (in $; N$)?

Two small spherical balls,each carrying a charge $Q = 10\,\mu C$ ($10$ micro-coulomb),are suspended by two insulating threads of equal lengths $1\,m$ each,from a point fixed in the ceiling. It is found that in equilibrium,the threads are separated by an angle of $60^o$ between them,as shown in the figure. What is the tension in the threads in $N$? (Given: $\frac{1}{4\pi \varepsilon_0} = 9 \times 10^9\,Nm^2/C^2$)

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

Four charges of magnitude $-Q$ are placed at the four corners of a square,and a charge $q$ is placed at the center. If the system is in equilibrium,the value of $q$ is ......

$A$ particle of mass $1 \, mg$ and charge $q$ is placed at the midpoint of two stationary particles,each carrying the same charge $q$,kept at a distance of $2 \, m$. If the free charged particle is displaced from its equilibrium position by a small distance $x$ $(x \ll 1 \, m)$,it executes $SHM$. Its angular frequency of oscillation will be $.... \times 10^{8} \, rad/s$ if $q^{2} = 10 \, C^{2}$.

In the given diagram,find the distance of the neutral point from the particle of charge $e$ in $cm$.