* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Theme 2: The story of Magnets
Electric motor wikipedia , lookup
Friction-plate electromagnetic couplings wikipedia , lookup
Electricity wikipedia , lookup
History of electromagnetic theory wikipedia , lookup
Lorentz force wikipedia , lookup
History of electrochemistry wikipedia , lookup
Hall effect wikipedia , lookup
Neutron magnetic moment wikipedia , lookup
Scanning SQUID microscope wikipedia , lookup
Magnetic nanoparticles wikipedia , lookup
Magnetic monopole wikipedia , lookup
Electromagnetism wikipedia , lookup
Earth's magnetic field wikipedia , lookup
Magnetic field wikipedia , lookup
Superconductivity wikipedia , lookup
Magnetic core wikipedia , lookup
Magnetohydrodynamics wikipedia , lookup
Electric machine wikipedia , lookup
Magnetoreception wikipedia , lookup
Multiferroics wikipedia , lookup
Magnetochemistry wikipedia , lookup
Galvanometer wikipedia , lookup
Faraday paradox wikipedia , lookup
Eddy current wikipedia , lookup
Force between magnets wikipedia , lookup
Open Text Material Class VI Subject - Science Theme 2: The story of Magnets 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. William Gilbert in 1600 first realized that the Earth was a giant magnet and that magnets could be made by beating wrought iron. He also discovered that heating resulted in the loss of induced magnetism. A magnet is any object that has a magnetic field. It attracts ferrous objects like pieces of iron, steel, nickel and cobalt. In the early days, the Greeks observed that the naturally occurring 'lodestone' attracted iron pieces. From that day onwards began the journey into the discovery of magnets. These days magnets are made artificially in various shapes and sizes depending on their use. One of the most common magnets - the bar magnet - is a long, rectangular bar of uniform crosssection that attracts pieces of ferrous objects. The magnetic compass needle is also commonly used. The compass needle is a tiny magnet which is free to move horizontally on a pivot. One end of the compass needle points in the North direction and the other end points in the South direction. The end of a freely pivoted magnet will always point in the North-South direction. The end that points in the North is called the North Pole of the magnet and the end that points South is called the South Pole of the magnet. It has been proven by experiments that like magnetic poles repel each other whereas unlike poles attract each other. Remember the force when you held two magnets close and felt them either attract (pull toward one another) or repel (push away)? One of the most amazing things about magnets is the way they can attract other magnets (or other magnetic materials) "at a distance," invisibly, through what we call a magnetic field. You might be surprised just how many things around you work by magnetism or electromagnetism. Every electric appliance with an electric motor in it (everything from your electric toothbrush to your lawn mower) uses magnets to turn electricity into motion. Motors use electricity to generate temporary magnetism in wire coils. The magnetic field thus produced pushes against the fixed field of a permanent magnet, spinning the inside part of the motor around at high speed. You can harness this spinning motion to drive all kinds of machines. There are magnets in your refrigerator holding the door closed. Magnets read and write data (digital information) on your computer's hard drive and on cassette tapes in old-fashioned personal stereos. More magnets in your hi-fi loudspeakers or headphones help to turn stored music back into sounds you can hear. If you're sick with a serious internal illness, you might have a type of body scan called NMR (nuclear magnetic resonance), which draws the world beneath your skin using patterns of magnetic fields. Magnets are used to recycle your metal trash. Steel food cans are strongly magnetic but aluminum drinks cans are not, so a magnet is used to separate the two different metals. Que.1) How was magnet first discovered? How was the first “man-made” magnet made? (3+2) Que.2) What are the properties of a magnet? Write the uses of magnets. (3+2)