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Magnetism notes Magnets can be made from loadstone (iron ore), Al, Co, Ni, or Electro Called - Permanent – it is hard to magnetize and demagnetize - Temporary – it is easy to magnetize and demagnetize *show loadstone two things that destroy mags - heat - jarring or banging The core of Earth is Fe therefore the earth is a magnet. Early as the 1600’s the Chinese were using magnets for Compasses *show compass Mags have two poles. North and South – Monopole mags do not exist Like poles repel, Unlike poles attract. *spin bar mag with horseshoe Magnetic Field (B) unit: Tesla “T” - goes from N to S - is created when polar molecules align themselves in the same direction - area in a substance where molecules are aligned are called domains ex. – 3 ½ floppy disk, music tape Electro Magnetism - when current is passed through a wire, a B-field is produced - two ways to make stronger, coil wire & use iron core - R-H-R Right Hand Rule Thumb is current Fingers are B-field *diagram * show coil can’t pick up paperclip w/o core *Show wire w/ 7A over compass, both parallel and perpendicular * Show compass in jar with coil A force will be on a wire that is in a mag field - F= B LI (force = mag field x length of wire x current) - add palm as force to R-H-R - * show move wire with mag- follow R-H-R schematic - w/o iron core - w/ iron core Several Names - solenoid - inductor - coil - electromag Several Uses - Store energy E= ½ LI2 L is for inductance measured in Henrys “H” - Peak voltage - Smooth out current - used as lightning protectors - magnet - Antenna - Phasor *Show spark plugs, neon glow bulb, and tesla coil *Show bell, trunk switch, speakers Induction is to create electricity in a wire by moving a magnet near a coil. Unit: Henrys Converts KE to EE Ex. Microphone *show galvanometer with coil and mag. * show mag dropped through a copper tube. EMF=BvL (voltage produced = Mag field x velocity x length of wire) DC Motors have a coil of wire in a mag field. The current it put through it so that the poles are opposite. And the coil turns. A system of commutators and brushes change the direction of current so that it continues this way. Generators are motors run backwards. *show cup motor *show genco gen/motor *show dc motor w/o cover *show Ac fan motor Transformers Change AC voltages. Step up - increase voltage Step down - decreases voltage Two coils work in mutual inductance. One creates a changing mag field, the other catches it and turns it into EE. Primary coil is the one EE goes into, Secondary Coil is the one EE comes out of The coil ratio is equal to the voltage ratio. Vs/Vp=Ns/Np *show transformer Ideally Pout = Pin , actually some gets converted into heat. Eff= Pout/Pin *do example prob