When two magnets are brought together, the opposite poles attract each other, called north and south poles, but like poles—two north poles or two south poles—will repel each other. Learn more about the nature of energy. Robert Norman, who lived from about to , was an instrument maker, and a British sailor for many years.
He became a maker of navigational instruments following his career as a sailor. Rather than simply duplicating the design of others, however, Norman attempted to improve the seagoing compass. He then wrote some of his experiences in a book called The Newe Attractive , published in And this described the curious tendency of a compass needle to dip.
The dip was somewhat of a nuisance to compass makers. This was the tendency of a compass needle not only to align itself north and south but also to adopt an angle dipping into the Earth. Norman described his experience and frustration in trying to make a compass needle. This is why he was trying to correct a particularly beautiful and decorated needle. What Norman did was a very clever idea. Intrigued, he began digging and discovered the first recorded lodestone.
In the early A. Pliny attributed the powers of magnetite to magic, launching years of superstitious theories about the material, including the possibility that ships that had disappeared at sea had actually been attracted to magnetic islands.
On an unrelated but interesting note, Pliny died in the eruption of Pompeii. With a large lodestone deposit in Scandinavia and not enough light to navigate ships by in the winter, the Vikings had plenty of incentive to put the magnetic properties of lodestone to practical use.
As early as 1, B. History tells us that Viking sailors utilized a magnetized iron needle placed into a piece of straw—and floated in a bowl of water—to indicate north and south. The Chinese navigated using a splinter of lodestone floated on water as early as A.
The name is originally from the ancient Greek word "lithos magnes". But this word probably comes more from the countryside Magnesia Magnisia in Thessaly, a famous locality of the magnetic stones. Other sources say the name was given by the city of Magnesia in Asia Minor a present-day region in Turkey.
She was a colony of the Magnet Macedonian tribe. The special characteristics of the magnetite were not only known by the ancient Greeks, the properties of the magnets were also analyzed in China in the pre-Christian times.
In the Warring States period Hanfuzius developed there the first compass ever. It consisted in a spoon shaped lodestone placed as a compass needle on a flat square bronze or copper plate in which symbols, lines and writings were engraved. The magnetic field of the spoon was aligned so that it pointed again to the south after each rotation.
The south was the preferred direction of the Taoist trigrams. It was the direction of the sky, while the north was considered inauspicious. In Europe the first description of the use of compasses for navigation was given by Alexander Neckam. The use of these needles gave the possibility to navigate in a complete darkness too.
On the contrary, Pierre de Maricourt mentioned for the first time a dry compass in his " Epistola de Magnete " written in He had free-swinging, dry magnetic needles, which rotated on a pin. The geomagnetic field generated will be dipolar in character, similar to the magnetic field in a conventional magnet, with lines of magnetic force lying in approximate planes passing through the geomagnetic axis.
The principle of the compass needle used by the ancient mariners involves the alignment of a magnetized needle along the Earth's magnetic axis with the imaginary south pole of the needle pointing towards the magnetic north pole of the Earth. The magnetic north pole of the Earth is inclined at an angle of 11 degrees away from its geographical north pole. Five basic types of magnetism have been observed and classified on the basis of the magnetic behavior of materials in response to magnetic fields at different temperatures.
These types of magnetism are: ferromagnetism, ferrimagnetism, antiferromagnetism, paramagnetism, and diamagnetism. Ferromagnetism and ferrimagnetism occur when the magnetic moments in a magnetic material line up spontaneously at a temperature below the so-called Curie temperature, to produce net magnetization. The magnetic moments are aligned at random at temperatures above the Curie point, but become ordered, typically in a vertical or, in special cases, in a spiral helical array, below this temperature.
In a ferromagnet magnetic moments of equal magnitude arrange themselves in parallel to each other. In a ferrimagnet, on the other hand, the moments are unequal in magnitude and order in an antiparallel arrangement.
When the moments are equal in magnitude and ordering occurs at a temperature called the Neel temperature in an antiparallel array to give no net magnetization, the phenomenon is referred to as antiferromagnetism.
These transitions from disorder to order represent classic examples of phase transitions. The magnetic moments-referred to as spins-are localized on the tiny electronic magnets within the atoms of the solid. Mathematically, the electronic spins are equal to the angular momentum the rotational velocity times the moment of inertia of the rotating electrons.
The spins in a ferromagnetic or a ferrimagnetic single crystal undergo spontaneous alignment to form a macroscopic large scale magnetized object. Most magnetic solids, however, are not single crystals, but consist of single crystal domains separated by domain walls.
The spins align within a domain below the Curie temperature, independently of any external magnetic field, but the domains have to be aligned in a magnetic field in order to produce a macroscopic magnetized object.
This process is effected by the rotation of the direction of the spins in the domain wall under the influence of the magnetic field, resulting in a displacement of the wall and the eventual creation of a single large domain with the same spin orientation.
Paramagnetism is a weak form of magnetism observed in substances which display a positive response to an applied magnetic field. This response is described by its magnetic susceptibility per unit volume, which is a dimensionless quantity defined by the ratio of the magnetic moment to the magnetic field intensity. Paramagnetism is observed, for example, in atoms and molecules with an odd number of electrons, since here the net magnetic moment cannot be zero.
Diamagnetism is associated with materials that have a negative magnetic susceptibility. It occurs in nonmagnetic substances like graphite, copper, silver and gold, and in the superconducting state of certain elemental and compound metals. The negative magnetic susceptibility in these materials is the result of a current induced in the electron orbits of the atoms by the applied magnetic field.
The electron current then induces a magnetic moment of opposite sign to that of the applied field. The net result of these interactions is that the material is shielded from penetration by the applied magnetic field. The magnetic field or flux density is measured in metric units of a gauss G and the corresponding international system unit of a tesla T.
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