Transcript Magnetism
Magnetism • What do you know about magnets? Misconceptions: History • The name magnetism comes from rocks, called lodestones, found in the region of Magnesia in Greece more than 2000 years ago. – 12th-century: Chinese used the rocks to navigate ships. – 18th century: Coulomb studied the forces between the stones. • We now know the lodestones contain iron ore – Electricity and Magnetism where thought of as completely unrelated until a professor was showing his class electric currents. – When an electric current passed near a compass the needle jumped. This baffled scientist for many years. Magnets • All magnets have a NORTH and a SOUTH pole • Cut a magnet in half, each half will have a north and south pole Poles • Bar Magnet • The poles are named due to the geographic direction that they will point if freely suspended and allowed to align with the Earth’s magnetic field. • The North Pole of a magnet will point northward geographically. It is NORTH SEEKING. • The South Pole of a magnet will point southward geographically. It is SOUTH SEEKING. Geographic Poles • Since the north pole of a magnet is attracted by the south pole of another magnet, it must be true that the magnetic pole in the northern hemisphere is actually the SOUTH MAGNETIC POLE of the Earth’s magnetic field. Sooo: • The geographic north pole is the south magnetic pole of the Earth, (and vice versa) Ferromagnetic Substances • Only substances that are Ferromagnetic can be magnetized. The four Ferromagnetic elements are: Iron (Fe) Gadolinium (Gd) Cobalt (Co) Nickel (Ni). Where does magnetism come from? • ALL MAGNETISM ARISES FROM MOVING ELECTRIC CHARGES!!!!! Magnetic Domains In an atom: • The spin of the electron creates a magnetic domain – A magnetic domain can be a cluster of atoms to billions of atoms • When the magnetic domains align, the substance is considered magnetic Iron Bar Unmagnetized vs. Magnetized How to create a temporary magnet 1. Place an object that is made of a ferromagnetic substance in a larger magnetic field. – The stronger magnet aligns the domains of the substance you want to become magnetized. 2. Rub an object over and over again in the same direction. Examples of temporary magnets A. “Survivor” B. Silverware in the dishwasher C. screwdriver How to destroy a magnet • To unalign the domains: 1. Drop the magnet 2. Heat the magnet 3. Expose the magnet to another magnetic field Magnetism and the Earth • Currently it’s thought that the Earth’s magnetic field arises from the convection currents in the mantle. • This explanation accounts for the geologic observation of the magnetic poles flip flopping several times over the history of the Earth. Drawing magnet field lines for the Earth: Remember: • Always draw magnetic field lines from NORTH to SOUTH • Drawing magnet field lines for the Earth: – Draw from southern hemisphere (magnetic north) to the northern hemisphere (magnetic south)