Dipole

Dipole, systems of two equal, connected electric charges. The product of the quantity of electricity (e) of one of the charges and the distance (d) between them is called the dipole moment (M); M=e.d. If the connection between the charges is rigid and the distance between them cannot change, then such a dipole has a constant dipole moment; all other dipoles are called dipoles with a variable dipole moment. An external electric field, acting on a dipole, turns it, causing it to orient itself such that the opposite pole of the dipole is turned toward the external charge (see figure). Such an oriented dipole will be attracted to the charge, since the like charge of the dipole is located farther away and therefore is repelled less strongly than ___________ the opposite charge is attracted. This attrac-

tion is directly proportional to the dipole moment and inversely proportional to the third power of the distance of the charge from the dipole. According to the modern theory of the structure of matter, molecules in many cases represent dipoles. A typical dipole is, for example, the water molecule, at one end of which are both positively charged hydrogen ions, and at the other end is the negative oxygen. The rotation of the water dipole described above in an electric field determines its dielectric constant (see Dielectrics), and the orientation and attraction to ions present in aqueous solution leads to their hydration (see). Many properties of substances (dielectric constant, refractive index, heat of dissociation, etc.) can be explained if molecules are considered as dipoles.