Magnet

1. Magnet A magnet (from Greek μαγνήτιςλίθοςmagnḗtislíthos, Magnesian stone) is a material or object that produces a magnetic field. This magnetic field is invisible but is responsible for the most notable property of a magnet: a force that pulls on other ferromagnetic materials like iron and attracts or repels other magnets.

2. A permanent magnet is an object made from a material that is magnetized and creates its own persistent magnetic field. An everyday example is a refrigerator magnet used to hold notes on a refrigerator door. Materials that can be magnetized, which are also the ones that are strongly attracted to a magnet, are called ferromagnetic (or ferrimagnetic). These include iron, nickel, cobalt, some alloys of rare earth metals, and some naturally occurring minerals such as lodestone. Although ferromagnetic (and ferrimagnetic) materials are the only ones attracted to a magnet strongly enough to be commonly considered magnetic, all other substances respond weakly to a magnetic field, by one of several other types of magnetism

3. An electromagnet is made from a coil of wire which acts as a magnet when an electric current passes through it, but stops being a magnet when the current stops. Often an electromagnet is wrapped around a core of ferromagnetic material like steel, which enhances the magnetic field produced by the coil.

4. The overall strength of a magnet is measured by its magnetic moment or the total MAGNETIC FLUX measured in WEBER in the SI system of units. while the local strength of the magnetism in a material is measured by its magnetization and or magnetic INTENSITY (TESLA)in the SI system of units.

5. History Of Magnets The Shepherd Magnes The most popular legend accounting for the discovery of magnets is that of an elderly Cretan shepherd named Magnes. Legend has it that Magnes was herding his sheep in an area of Northern Greece called Magnesia, about 4,000 years ago. Suddenly both, the nails in his shoes and the metal tip of his staff became firmly stuck to the large, black rock on which he was standing. To find the source of attraction he dug up the Earth to find lodestones (load = lead or attract). Lodestones contain magnetite, a natural magnetic material Fe3O4. This type of rock was subsequently named magnetite, after either Magnesia or Magnes himself.

6. The Greek & Chinese The earliest discovery of the properties of lodestone was either by the Greeks or Chinese. Stories of magnetism date back to the first century B.C in the writings of Lucretius and Pliny the Elder (23-79 AD Roman). Pliny wrote of a hill near the river Indus that was made entirely of a stone that attracted iron. He mentioned the magical powers of magnetite in his writings. For many years following its discovery, magnetite was surrounded in superstition and was considered to possess magical powers, such as the ability to heal the sick, frighten away evil spirits and attract and dissolve ships made of iron! People believed that there were whole islands of a magnetic nature that could attract ships by virtue of the iron nails used in their construction. Ships that thus disappeared at sea were believed to have been mysteriously pulled by these islands. Archimedes is purported to have used loadstones to remove nails from enemy ships thus sinking them. People soon realized that magnetite not only attracted objects made of iron, but when made into the shape of a needle and floated on water, magnetite always pointed in a north-south direction creating a primitive compass. This led to an alternative name for magnetite, that of lodestone or "leading stone".

7. Oersted & Maxwell In 1820 Hans Christian Oersted (1777-1851 Danish) demonstrated that magnetism was related to electricity by bringing a wire carrying an electric current close to a magnetic compass which caused a deflection of the compass needle. It is now known that whenever current flows there will be an associated magnetic field in the surrounding space, or more generally that the movement of any charged particle will produce a magnetic field. Eventually it was James Clerk Maxwell (1831-1879 Scottish) who established beyond doubt the inter-relationships between electricity and magnetism and promulgated a series of deceptively simple equations that are the basis of electromagnetic theory today. What is more remarkable is that Maxwell developed his ideas in 1862 more than thirty years before J. Thomson discovered the electron in 1897, the particle that is so fundamental to the current understanding of both electricity and magnetism.

8. Magnetic Fields The space surrounding a magnet, in which magnetic force is exerted, is called a magnetic field. If a bar magnet is placed in such a field, it will experience magnetic forces. However, the field will continue to exist even if the magnet is removed. The direction of magnetic field at a point is the direction of the resultant force acting on a hypothetical North Pole placed at that point.

12. Properties of the magnetic lines of force * The magnetic lines of force originate from the North Pole of a magnet and end at its South Pole. * The magnetic lines of force come closer to one another near the poles of a magnet but they are widely separated at other places. * The magnetic lines of force do not intersect (or cross) one another. * When a magnetic compass is placed at different points on a magnetic line of force, it aligns itself along the tangent to the line of force at that point.

13. Industrial Uses of Magnets Uses Of Magnets in Industry From Lodestone being used as a mariner's compass to magnetic therapy - magnets have come a long way. Magnets are used in various industries all over the world in various forms. Televisions Televisions have magnets inside of them that make them work. These cathode ray tubes have an electron gun in the neck of the tube that shoots a stream of electrons toward the screen. Normally these electrons travel in a straight line and strike the screen at a central spot. But powerful electromagnets in the tube's neck deflect the electrons toward the top or bottom and left or right sides of the tube. The inside of the screen has a special coating that glows when the stream of electrons strikes it. In this way, magnets help us see images on the TV screen.

15. Computer Disks Computer storage disks are coated with an iron material that stores tiny magnetic fields in a pattern, and that is how we store data on the computer disks. Computer screens also use magnets in a manner similar to televisions. Video Tapes Video tapes also use a similar material with iron compounds that allows magnetic fields to be stored in patterns on the tape. Magnetic Sweepers Magnetic sweepers are used in industries to help reduce maintenance costs and eliminate flat tires at airports, loading docks and work sites. Sorters Magnets can also be used for sorting magnetic material from non-magnetic material. Magnets are used in the mining industry to separate metals from ore. Food manufacturers use magnets to prevent small iron particles from mixing with the food. Similarly vendors use magnets to separate coins from other junk.

16. Maglev Trains Maglev trains operate without wheels as they 'float' above the track due to magnetic repulsion between electromagnets in the track and underside of the train. Maglev trains can travel very fast, up to 480 km/h (300 mph). These Maglev trains were launched in Japan, in 1997, and clocked at an incredible 343 miles an hour! Credit Cards and Other ID Cards Magnets are also used to make the everyday credit cards and other forms of ID that we use. Around the house Magnets are used around the house in innumerable things some of which are: Headphones, Stereo speakers, Computer speakers, Telephone receivers, Phone ringers, Microwave tubes, Doorbell ringer solenoid, Refrigerator magnets to hold things, Seal around refrigerator door, Plug-in battery eliminators, TV deflection coil, TV degaussing coil, Computer monitor deflection coil, Computer hard drive recording and reading head, Dishwasher water valve solenoid, Shower curtain weights / attach to tub, Power supply transformers and many more!