Monopole

A monopoly ( the monopoly, emphasis on the first syllable of ancient Greek μόνος ( monos ) = "alone" and Greek πόλος Polos " axis ", " axis point " ) as a physical concept is a single pole, for example, an electric point charge.

Use of the term

As the first order in the multipole expansion of a field describes the electric field of the reduced to a point total charge of an electric charge distribution of a monopole field, for example. The monopole field is distinguished from the higher orders by its isotropy.

The magnetic monopole is a hypothetical elementary particle or quasi-particles in certain solids, which behaves like a single magnetic pole.

In Yang-Mills theories ( gauge theories with gauge groups that have non-commutative elements ) some stable, characterized by topological invariants solutions of the field equations are also called (magnetic) monopoles. Electromagnetism is just a special case of a theory ( unitary group); other theories can certainly monopolies for both equivalents of electric and magnetic fields exist.

Sometimes an antenna design in which only one half of a dipole antenna ( usually upright ) out of the earth is called a " monopoly " is. However, here take the name also used "half dipole " better, because it has the same directivity. An antenna directivity without the hypothetical isotropic radiator.