Dipoles and monopoles

A pair of magnetic poles is called a dipole. A lone pole, like the positive pole in a proton, is called a monopole.
Magnetic monopoles do not ordinarily exist in nature. If they could somehow be conjured up, all sorts of fascinating things might happen. Scientists are researching this to see if they can create artificial magnetic monopoles.
At first you might think that the magnetic field around a current-carrying wire is caused by a monopole, or that there aren’t any poles at all, because the concentric circles don’t actually converge anywhere. But in fact, you can think of any half-plane, with the edge along the line of the wire, as a magnetic dipole, and the lines of flux as going around once from the “north face” of the half-plane to the “south face.”
The lines of flux in a magnetic field always connect the two poles. Some flux lines are straight; some are curved. The greatest flux density, or field strength, around a bar magnet is near the poles, where the lines converge. Around a current-carrying wire, the greatest field strength is near the wire.