 Always have two poles  1 pole seeks north, other seeks south  Like poles  repulsive  Unlike  attractive  All magnets have two poles

 Direction of force when magnet is placed in someone else’s location  Usually a compass  Extends from pole to pole, N  S  Iron (or other magnets) tend to line up parallel to field  Recall how electric fields were generated

 Moving electric charges generate a magnetic field  Stationary = only electric fields  Atoms have moving electrons  magnetism  Somehow (?) spinning electrons create magnetism  Materials in which spins “coordinate” can become magnetic – Fe, Ni, Co

 Clusters of aligned atoms – have same relative magnetic field  Presence of magnetism near Fe “forces” an alignment – creating temporary magnet  Permanent magnet – domains stay in place after field is removed

 Moving charges experience forces w/I magnetic fields  Greatest when perpendicular, zero when parallel  Direction of force is perpend. to field & velocity of charge  Found by using right hand rule  Particles can be steered by mag. Fields  Old style TV’s & Earth

 Since moving charges produce magnetism so do electric currents  Field is not radial  Field forms circles around conductor

 If wire forms a loop, the field lines are concentrated in the center of loop  Doubling loops – double field strength  Many loops form an electromagnet  Iron placed inside loop coils intensifies magnetic field  Most powerful electromagnets – superconducting

 Current (moving charges) also causes a deflection (force) on wires  Again perpendicular to field & direction of current  Parallel wire with field = no deflection  Symmetry: current deflects magnetic compass & magnets deflect current carrying wires

Galvanometers  Magnetic needle inside loops of wire indicates current – galvanometer  The more coils – the more sensitive  Can be made into a ammeter or voltmeter

 Electric motor = galvanometer made to change current direction with every half rotation  Current flow in opposite directions causes forces in opposite directions

 The earth acts as a giant magnet  Geographic/Magnetic poles do not line up  Difference between = magnetic declination  “current” theory – liquid inside (core) is flowing creating magnetism  Magnetism has “switched” (reversed) many times in the past