An electric dipole has the magnitude of its charge as q and its dipole moment is p. It is placed in a uniform electric field E. If its dipole moment is along the direction of the field, the force on it and its potential energy are respectively

When is an electric dipole in a stable equilibrium in a uniform electric field.

Three charges $+2q, -q$ are $\mathit{-}q$  are placed at the vertices $A, B$ and $C$ respectively of an equilateral triangle $ABC$ of side $a$. Find the magnitude of dipole moment of this system.

Demonstrate that the potential of the field generated by a dipole, with electric moment $\overrightarrow{\mathit{P}}$, may be represented as $\mathrm{\phi }=\frac{\overrightarrow{p}·\overrightarrow{r}}{4\mathrm{\pi }{\epsilon }_0{r}^3}$, where $\overrightarrow{\mathit{r}}$ is the radius vector. Using this expression, find the magnitude of the electric field strength vector as a function of $r$ and $\mathrm{\theta }$.