Magnetism.ppt

Magnetism Magnetic Poles Magnets exert force on one another Regions of magnetic poles produce magnetic forces The end that points northward is called the north-seeking pole and vice-versa Each magnet has both poles-even if you take a magnet and break it in two, each part will have both poles Likes poles repel; opposite poles attract Electric charges can be isolated, magnetic poles cannot Magnetic Fields The space around a magnet in which a magnetic force is exerted, is filled with a magnetic field The shape of the field is revealed by magnetic field lines Magnetic Domains: The magnetic field of individual iron atoms is so strong that interactions among adjacent iron atoms cause large clusters of them to line up with each other. These clusters of aligned atoms are called magnetic domains The difference between a piece of ordinary iron and an iron magnet is alignment of domains Permanent magnets are made by simple placing pieces of iron or certain iron alloys in strong magnetic fields The Nature of a Magnetic Field A magnetic field is produced by the motion of electric charge The magnet as a whole is stationary while the electrons are in constant motion Every spinning electron is a tiny magnet The Earth’s Magnetic Field The discrepancy between the orientation of a compass and true north is called the magnetic declination The magnetic field of the earth is not stable Oersted’s Discovery In a public experiment, Oersted showed that electric current could affect the motion of a compass needle The effect decreases by distance, but is not affected by blockage by other materials(glass,paper,water, even metal) The effect on a compass is a torque, proportional to field strength B and magnetic dipole moment m so that t=mBsinq Units for field strength = tesla symbolized T Direction of the field around the wire is in concentric circles rotationg according to a right-hand rule : If the thumb of the right hand is in the direction of the current, the curling fingers sh