Write the expression for the torque experienced by an electric dipole placed in a uniform electric field.

Three charges $q, -2q$ and $q$ are placed at $(x=0, y=a, z=0)$,$(x=0, y=0, z=0)$ and $(x=a, y=0, z=0)$ respectively. What is the resultant electric dipole moment?

Two point dipoles of dipole moments $\vec{p}_1$ and $\vec{p}_2$ are at a distance $x$ from each other,and $\vec{p}_1 \parallel \vec{p}_2$. The force between the dipoles is:

The ratio of electric fields on the axis and at the equator of an electric dipole is

The relation between the intensity of the electric field of an electric dipole at a distance $r$ from its centre on its axis and the distance $r$ is . . . . . . . (where $r \gg 2a$)

Two small spherical balls of mass $10 \ g$ each with charges $-2 \ \mu C$ and $2 \ \mu C$,are attached to two ends of a very light rigid rod of length $20 \ cm$. The arrangement is now placed near an infinite nonconducting charge sheet with a uniform charge density of $100 \ \mu C / m^2$ such that the length of the rod makes an angle of $30^{\circ}$ with the electric field generated by the charge sheet. The net torque acting on the rod is (Take $\varepsilon_0 = 8.85 \times 10^{-12} \ C^2 / Nm^2$) (in $Nm$)