What is a dipole moment?

Let us consider, as applied to electrodynamics, what a dipole moment is. Elementary charge carriers flowing along a straight section of the conductor system form a direct current. Accordingly, there is a current charge of the indicated current (I * L, where I is the current value, L is the length of the section). In turn, Ampere's law considers two parallel current charges for L, tending to infinity. In a closed loop, its two halves have opposite current in the direction forming a current dipole. A vortex field is created around each such dipole, which has its own dipole current charge, oriented perpendicular to the plane in which the contour is located. It is called the dipole moment. But since we are considering only the current component, then for the transition to electromagnetism the same term is called otherwise. Another name is the magnetic dipole moment (Pm, sometimes just m).

It is one of the key characteristics of any substance. It is believed that the dipole moment arises from currents (both in the microworld and in macrosystems). Under the microworld in this case we mean an atom: charges (electrons) moving in circular orbits can be considered as an electric current. Since the substance consists of elementary particles, each of them also has its own moment. We draw attention to the fact that by elementary particles we need to understand not only molecules and atoms, but also protons, neutrons, electrons and, possibly, even smaller components. From the point of view of quantum mechanics, their magnetic dipole moment is due to their own mechanical rotation - spin. However, this assumption has recently been increasingly questioned in the light of the latest field theory of particles. For example, the existence of the so-called anomalous dipole, whose value differs from the calculations of the equation in quantum theory, is universally recognized. But from the field point of view, in which the magnetic field of any elementary particle is generated not by the spin rotation of the charge carriers, but is one of the constant components of the electromagnetic field, the anomalous dipole is easily explained. The value is defined as a certain set of quantum numbers with the correcting component of the spin. Thus, the magnetic moment for a neutron depends on the electric current generating it and on the energy of the changing electromagnetic field.

When calculating its value for an entire circuit, the method of integral addition of the dipole moments of the simplest current dipoles, which create a closed circular contour, is used.

The dipole moment in electrodynamics is determined by the formula:

Pm = S * I * n,

Where I is the value of the flowing current; S is the area of the closed loop (circular); N is a vector directed perpendicular to the plane in which the contour is located. Although the above formula does not show this, the value of Pm is also vector, the directivity of which can be determined by the rule of the drill (right-handed screw) known in classical engineering: if the rotation of the imaginary screw is compared with the direction of the flowing current, the motion of the body of the screw will coincide with the desired vector.

The electric field of a dipole differs from the field of a point charge, first of all, by the configuration of lines of force. Since from the point of view of physics such a dipole is a balanced system of two electric charges, whose moduli are equal, and the polarity is opposite (+ and -), then the corresponding tension lines start at one charge, and end in the other. In the case of only one point charge carrier, the lines diverge in all directions, like the light of a lamp.