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5.12 MAGNETISM p163 Magnet = is an object that can attract another object. Contains iron, cobalt and/or nickel Magnetism = is the phenomena caused by magnets History of Magnetism Observed by the Greek 600 BC Put into use by the Chinese Used by magicians and sailors Illusions….. Always, sometimes or never???? Iron is sometimes magnetic. ST EST AST Iron is made up of domains that are like tiny magnets. When the iron is not magnetized, the domains are not aligned. Their magnetic effects cancel out. When the iron is magnetized, the domains line up. The greater the number of aligned domains, the stronger the magnet. ST EST AST Magnets will always have a north and a south pole. If the magnet breaks, each piece will have a north and a south. Categories of Substances Three Categories Magnetic Ferromagnetic Non-magnetic Magnetic Invisible fields Attract or repel Object that has a field and that can attract some other objects. Example: horseshoe magnet Ferromagnetic Not a magnet Is attracted by a magnet Can be magnetized (by a magnet) Must contain iron, nickel or cobalt eg: paper clip or nail Non-Magnetic Is not attracted by a magnet Example: glass, plastic, or wood Magnetism is a property that makes certain materials attract or repel. Permanent Magnet is always magnetic creates a magnetic field Ferromagnetic Attracted by a magnet, can become magnetized Must contain Iron, Nickel, Cobalt Nonmagnetic Never attracted by a magnet Important Facts about Magnets Facts: All magnets have two poles, a North (N) and a South (S). They are known as dipoles. Fields are infinite in size & 3-Dimensional Repulsion Important Similar poles repel & opposite poles attract. Attraction Important Poles N attracts South S attracts North N repels North S repels South Opposites attract Likes repel Mapping Magnetic Fields Remember •the lines never cross Around a magnet there are lines of goes from North to South force•Always that have direction and strength •Closer the lines, stronger the attraction (magnetic field). Compass The needle of the compass is magnetic Important Example #1 Example #2 North end Red Tip of needle is North Red Tip will always be attracted towards the South end. Tip of arrow Is North therefore It is attracted to South Opposites attract (i.e N & S) Likes Repel (i.e. S & S or N & N) Magnetic Field Arrows always go from north to south (outside magnet) Lines of force never cross The closer the lines, the stronger the field Compass Red portion of compass needle is a North ended magnet and is always attracted to the South end(of another magnet) Why the Compass Works Why the Compass Works Aurora Borealis NASA – explanation and history of northern lights http://youtu.be/ZqqTiiCgyUc Making own compass http://youtu.be/ZGaQXx5lDWo Origins of Magnetism of Matter Scientists believe that magnetism comes from spinning electrons around the nucleus of the atom. When atoms clump together they form a domain. Origins of Magnetism of Matter Similar electron spins produce a strong domain, where as opposite electron spins cancel one another out and produce a weak domain. If enough domains align in the same direction, this will create a magnetic field. 5.13 How to Magnetize an Object Bring the ferromagnetic substance in contact with another magnet. Bang the ferromagnetic substance (example: striking a nail repeatedly). Heat up the substance and cause the domains to align. Run electric current through the ferromagnetic substance. Please note that all of these methods can also de-magnetize a magnet. Some cool magnet stuff How to make a compass http://youtu.be/pjQU3yClEKU Ferrofluid http://youtu.be/HQzEBBmF960 http://youtu.be/1EuyZ5Lml4k Use the magnet boxes to help you draw the magnetic fields present in the following situations.