Magnetism & Electromagnetism - The Power of Attraction (Magnets)

• published: 29 Oct 2014
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"Magnets" reveals the essential role magnets play in today's society - from powering high-speed trains and theme-park rides to generating electricity and creating mechanical power, and also providing the basis for computers and data storage.The video begins by demonstrating how linear synchronous motors (change polarity in sync with the motion of a vehicle) work and allow a theme-park ride to reach 100 mph in 7 seconds, and maglev trains speeding 270 mph.Viewers also see iron filings used to reveal magnetic lines of force, and electromagnets used to separate materials in a junk yard. Then its on to an understanding of how electromagnets are built and operated, followed by the creation of more mundane "refrigerator" magnets.We also learn how the earth's magnetic field shields us from lethal cosmic bombardment.Man's awareness of magnetism began about 2,000 years ago when the Greeks and Chinese both discovered lodestones (magnetite); today's experts believe its magnetism is created by lightning strikes. Generating electricity and then power from the electricity are key to man's current standard of living.Various alloys have been found to make stronger magnets; rare-earth magnets help create miniature disc drives for today's laptops. The strongest magnetic field is a neutron star - up to 1,000 trillion times that of earth.Researchers now are looking at plastic magnets whose strength can be altered with various colors of laser light. NASA is also hopeful that magnet fields can be used to contain the hot gases created by plasma propulsion, thus lowering considerably the costs of space travel.A magnet 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, such as iron, and attracts or repels other magnets.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.Ferromagnetic materials can be divided into magnetically "soft" materials like annealed iron, which can be magnetized but do not tend to stay magnetized, and magnetically "hard" materials, which do. Permanent magnets are made from "hard" ferromagnetic materials such as alnico and ferrite that are subjected to special processing in a powerful magnetic field during manufacture, to align their internal microcrystalline structure, making them very hard to demagnetize. To demagnetize a saturated magnet, a certain magnetic field must be applied, and this threshold depends on coercivity of the respective material. "Hard" materials have high coercivity, whereas "soft" materials have low coercivity.An electromagnet is made from a coil of wire that acts as a magnet when an electric current passes through it but stops being a magnet when the current stops. Often, the coil is wrapped around a core of "soft" ferromagnetic material such as steel, which greatly enhances the magnetic field produced by the coil.The overall strength of a magnet is measured by its magnetic moment or, alternatively, the total magnetic flux it produces. The local strength of magnetism in a material is measured by its magnetization. We played with them as children, but the world of magnets isn't kid's stuff! The pervasive magnet serves as the underpinning for much of modern technology. They can be found in computers, cars, phones, VCRs, TVs, vacuum cleaners, the washer and dryer, the ubiquitous refrigerator magnet, and even in an electric guitar! On the cutting edge of technology, scientists experiment with a variety of magnets. Magnets' amazing forces of attraction and repulsion may some day take us to the far reaches of outer space. This documentary reveals the essential role magnets play in today's society - from powering high-speed trains and theme-park rides to generating electricity and creating mechanical power, and also providing the basis for computers and data storage.