Download Magnetism notes

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