Electric Dipole: Definition, Field & Moment | StudySmarter

At a first glance, electric dipoles seem like one of the electrostatic phenomena we don’t come across too often in our daily lives; however, electric dipoles actually appear more commonly than you might have first thought. Analysing the disturbance of the balance of positive and negative charges in an electric dipole and finding their polarity provides us with a better understanding of concepts such as contact forces, dielectrics and the behaviour of molecules. Electric dipoles are especially relevant when it comes to microscopic systems such as the dipoles found in molecules, which are far too close together to notice the effects of on a macroscopic scale, yet have very distinguishable charges. Before we dive into understanding what an electric dipole is and the closely related electric dipole moment, we will want to first establish some useful concepts like Coulomb’s forces and dielectrics.

What is a conductor?

A conductor is a substance that facilitates the free flow of charged particles. Substances containing a relatively large number of free charge carriers are called conductors. Metals, for instance, are considered good electrical conductors. In metals, electrons can move freely as they’re not bound to the metal’s crystal lattice and hence are free charge carriers. Let’s imagine a metal rod placed in an electric field equal to zero \((E=0)\). In such a case, electrons are uniformly distributed over the metal rod’s surface. Now, if we place the same rod into an electric field not equal to zero, all of the free charge carriers will move to one end of the object caused by the electric force experienced by the charge carriers due to the Coulomb force.

The Coulomb force is the force which acts between two point charges causing them to attract or repel each other in a vacuum, and can be expressed as:

$$F=k\frac{\left|q_1\right|\left|q_2\right|}{r^2}.$$

The constant of proportionality \(k\) is known as Coulomb’s constant:

$$k=\frac1{4\pi\varepsilon_0}=8.99\times10^9\;\mathrm{Nm}^2\mathrm C^{-2}$$

Coulomb’s force is proportional to the product of the magnitude of two point charges (\(q_1\) and \(q_”\)) and inversely proportional to the distance \(r\) between the charges squared. In other words, as the distance between two point charges increases, the force between them decreases with the square of their separation. This phenomenon is called electrostatic induction and results in the separation of negative and positive charges in a conductor.