Information AboutMagnetic Pole |
| CATEGORIES ABOUT MAGNET | |
| types of magnets | |
| mechanical biological treatment | |
| waste treatment technology | |
|
A magnet is an object that has a Magnetic Field . The word ''magnet'' comes from the Greek ''μαγνήτης λίθος'' (''magnētēs lithos''), which means "magnesian stone". Magnesia was an area in Ancient Greece , in present-day Manisa , Turkey where deposits of Magnetite have been discovered since antiquity. INTRODUCTION In the modern sense, a magnet is a material that has a es and even the vacuum of Outer Space . The SI unit of magnetic field strength is the Tesla , and the SI unit of total Magnetic Flux is the Weber . 1 weber = 1 tesla flowing through 1 square meter, and is a very large amount of magnetic flux. PHYSICAL ORIGIN OF MAGNETISM Permanent magnets All normal matter is composed of particles such as Proton s, Neutron s and Electron s, and all of these have the fundamental property of Quantum Mechanical Spin . Spin gives each one of these particles an associated magnetic field. Because of this, and the fact that the average microscopic piece of matter contains huge numbers of these particles, it would be expected that all matter would be magnetic. Even Antimatter would have magnetic characteristics. However, everyday experience shows that this is not the case. Within each atom and molecule, the spin of each of these particles is highly ordered as a result of the Pauli Exclusion Principle . However, there is no long range ordering of these spins ''between'' atoms and molecules. Without long range ordering, there is no net magnetic field because the magnetic moment of each one of the particles is cancelled by the magnetic moment of other particles. Permanent magnets are special in that long range ordering does exist. The highest degree of ordering exists within Magnetic Domain s. These domains can be likened to microscopic neighbourhoods in which there is a strong reinforcing interaction between particles, and as a result, a great deal of order. The greater the degree of ordering within and between domains, the greater the resulting field will be. Long range ordering (and the resulting strong net magnetic field) is one of the hallmarks of a Ferromagnetic material. Electronic generation of magnetism Electrons play the primary role in generating a magnetic field. Within an atom, electrons can exist either individually or in pairs within any given Orbital . When they are paired, the individuals in that pair always have opposite spin — one up, one down. The fact that the spins have opposite orientation means that the two cancel one another. If all electrons are paired, no net magnetic field will be generated. In some atoms, there are electrons that are unpaired. All magnets have unpaired electrons, but not all atoms with unpaired electrons are ferromagnetic. In order for the material to become ferromagnetic, not only must there be unpaired electrons present, but those unpaired electrons must interact with one another over long ranges such that they are all oriented in the same way. The specific Electron Configuration of the atoms (as well as the distance between atoms) is what leads to this long range ordering. The electrons find that they can exist in a lower energy state if they all have the same orientation. Electromagnets An Electromagnet , in its simplest form, is a wire that has been coiled into one or more loops. This coil is known as a Solenoid . When electric current flows along the coil, a magnetic field is generated around the coil. The orientation of this field can be determined via the Right Hand Rule . The strength of the field is influenced by several factors. The number of loops determines the Surface Area of interaction, the amount of current determines the amount of activity, and the material in the core determines Electrical Resistance . The more loops of wire and the greater the current, the stronger the field will be. If the coil of wire is empty in the center, it will tend to generate a very weak field. Different Ferromagnetic or Paramagnetic items can be placed in the center of the core with the effect of magnifying the magnetic field, for example an iron nail. In addition, soft iron is commonly used for this purpose. The addition of these types of materials can result in a several hundred- to thousand-fold increase of field strength. At long distances, magnetic fields obey an Inverse Square Law . This means that the field strength is inversely proportional to the square of the distance from the magnet. In the case of an electromagnet in contact with a flat metal plate, the force needed to separate the two will be greatest if the two surfaces are machined as flat as possible. The flatter the surfaces, the more points of contact between them, and the smaller the magnetic circuit's Reluctance to the magnetic field. Electromagnets find uses in many places, ranging from Particle Accelerator s, to junkyard cranes, to Magnetic Resonance Imaging machines. There are also specialized applications that involve more than a simple magnetic dipole, such as the Quadrupole Magnet s used to focus particle beams. If an electromagnet is strong enough, the magnetic force between neighbouring loops of wire can cause the electromagnet to be crushed by its own magnetic field. CHARACTERISTICS OF MAGNETIC MATERIALS Permanent magnets and dipoles All magnets have at least two poles: that is, all magnets have at least one north pole and at least one south pole. The poles are not a pair of things on or inside the magnet. They are a concept used to discuss and describe magnets. In the image at the top of this page, the poles look like specific locations, because the highest surface intensity of the field occurs at the poles), but this does not mean that they are specific locations. To understand the concept of pole, it can be imagined that a row of people who are all facing the same direction and standing in line. While there is a "face" end of the line and a "back" end of the line, there is no one place where all of the faces are and all of the backs are. The person at the front of the face end has a back; and the person at the back end has a face. If the line is divided into two shorter lines, each one of the shorter lines still has a face end and a back end. Even if the line is pulled completely apart so that there are just individuals standing around, each one of the individuals still has a face and a back. This can continue without end. The same holds true with magnets. There is not one place where all of the north or south poles are. If a magnet is divided in two, two magnets will result--and both magnets will have a north and a south pole. Those smaller magnets can then be divided, and all of the resulting pieces will have both a north and south pole. In most instances, if the material continues to be broken into smaller and smaller pieces there will be a point where the pieces are too small to retain a net magnetic field. They won't become individual north or south poles though; instead, they will just lose the ability to maintain a net field. Some materials, however, can be divided down to the Molecular Level and still maintain a net field with both a north and a south pole. There are theories involving the possibility of north and south Magnetic Monopole s, but no magnetic monopole has ever been found. North-south pole designation and the Earth's magnetic field A standard naming system for the poles of magnets is important. Historically, the terms north and south reflect awareness of the relationship between magnets and the Earth's Magnetic Field . A freely suspended magnet will eventually orient itself north-to-south, because of its attraction to the north and south magnetic poles of the earth. The end of a magnet that points toward the Earth 's geographic North Pole is labeled as the north pole of the magnet; correspondingly, the end that points south is the south pole of the magnet. The Earth's current ''geographic north'' is thus actually its ''magnetic south''. Confounding the situation further, magnetised rocks on the ocean floor show that the Earth's magnetic field has Reversed Itself in the past, so this system of naming is likely to be backward at some time in the future. Fortunately, by using an electromagnet and the Right Hand Rule , the orientation of the field of a magnet can be defined without reference to the Earth's geomagnetic field. To avoid the confusion between geographic and magnetic north and south poles, the terms ''positive'' and ''negative'' are sometimes used for the poles of a magnet. The positive pole is that which seeks geographical north. COMMON USES FOR MAGNETS
MAGNETIZATION OF MATERIALS Ferromagnetic materials can be magnetised in the following ways:
DEMAGNETIZING MATERIALS Permanent magnets can be demagnetized in the following ways:
In an electromagnet, ceasing the flow of current will eliminate the magnetic field. However, a slight field may remain in the core material as a result of Hysteresis . TYPES OF PERMANENT MAGNETS
MAGNETIC FORCES Magnetized items interact with other items in very specific ways. Forces between magnets If two magnets are brought close enough together, their fields will begin to interact in the following ways:
Magnets and ferromagnetic materials If a magnet is brought close enough to a Ferromagnetic material (that is not magnetized itself), the magnet will strongly attract the ferromagnetic material regardless of orientation. Both the north and south pole of the magnet will attract the other item with equal strength. Magnets and diamagnetic materials By definition, Diamagnetic materials weakly repel a magnetic field. This occurs regardless of the north/south orientation of the field. Magnets and paramagnetic materials By definition, Paramagnetic materials are weakly attracted to a magnetic field. This occurs regardless of the north/south orientation of the field. Calculating the magnetic force Calculating the attractive or repulsive force between two magnets is, in the general case, an extremely complex operation, as it depends on the shape, magnetization, orientation and separation of the magnets. Force between two monopoles The force between two magnetic monopoles is as follows: : {Link without Title} where :F is force (SI unit: Newton ) :m is pole strength (SI unit: Weber ) :μ is the Meter per Ampere ) :r is the separation (SI unit: meter). Since magnetic monopoles are only a theoretical construction, this equation does not describe a physically realisable arrangement. It is stated here because it is the simplest possible calculation of magnetic forces. In reality, one of the more complex formulae given below will be more useful. Force between two very close attracting surfaces : {Link without Title} where A B Force between two bar magnets The force between two identical cylindrical bar magnets placed end-to-end is given by: : [http://instruct.tri-c.edu/fgram/web/Mdipole.htm] where B0 A L R x SEE ALSO
ONLINE REFERENCES
PRINTED REFERENCES
EXTERNAL ARTICLES
|
|
|