Pole Magnetic

Pole, Magnetic. Those portions of the earth's surface to which the magnetic needle points are known as the magnetic north and south poles; they are not quite fixed in position, nor do they coincide with the ends of the earth's axis. The poles of a magnet are those portions of its surface at which lines of magnetic force leave the iron or steel; they are therefore the portions at which magnetic effects are apparent. That pole of a magnet which tends to point to the north is commonly known as its north pole, although, as unlike poles attract each other, it is clearly opposite in polarity to the terrestrial north pole. A magnet has usually two poles, but may have more - say, a north pole at each end and a south pole in the middle; the latter is in such a case called a consequent pole. Since a coil of wire acts as a magnet, it also has poles. If on looking at one end of a solenoid the current flows in the same direction as the motion of the hands of a clock, then the end looked at will be'the south pole. The unitmagnetic pole is defined as one of such strength that it repels an equal pole at a distance of one centimetre with a force of one dyne.