(N/A) The torque $\vec{\tau}$ experienced by an electric dipole in a uniform external electric field $\vec{E}$ is given by the cross product of the dipole moment $\vec{p}$ and the electric field $\vec{E}$:
$\vec{\tau} = \vec{p} \times \vec{E}$
In terms of magnitude,this is expressed as:
$\tau = pE \sin \theta$
where $\theta$ is the angle between the dipole moment vector $\vec{p}$ and the electric field vector $\vec{E}$.
To define the electric dipole moment,consider the case where the dipole is placed perpendicular to the electric field,i.e.,$\theta = 90^\circ$. Since $\sin 90^\circ = 1$,the torque becomes:
$\tau = pE$
Rearranging for $p$,we get:
$p = \frac{\tau}{E}$
Thus,the electric dipole moment is defined as the torque experienced by an electric dipole when it is placed perpendicular to a unit uniform electric field.