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???? ST EST AST  Iron is sometimes magnetic. 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.

 Magnets will always have a north and a south pole.  If the magnet breaks, each piece will have a north and a south. ST EST AST

Categories of Substances  Three Categories Magnetic Ferromagnetic Non-magnetic

Magnetic  Object that has a field and that can attract some other objects. Example: horseshoe magnet Invisible fields Attract or repel

Ferromagnetic  Is attracted by a magnet  Can be magnetized (by a magnet)  Must contain iron, nickel or cobalt eg: paper clip or nail Not a magnet

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  Similar poles repel & opposite poles attract. Repulsion Attraction Important

Poles N attracts South S attracts North N repels North S repels South Important Opposites attract Likes repel

 Around a magnet there are lines of force that have direction and strength (magnetic field). Mapping Magnetic Fields Remember the lines never cross Always goes from North to South Closer the lines, stronger the attraction

Compass  The needle of the compass is magnetic Red Tip of needle is North Red Tip will always be attracted towards the South end. Important North end Example #1 Example #2 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 Making own compass

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.

 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. Origins of Magnetism of Matter

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   Ferrofluid  

Use the magnet boxes to help you draw the magnetic fields present in the following situations.