Magnetism and Electromagnetism

3 types of magnets

natural, permanent, electromagnets

Natural magnets

magnets that naturally occur in nature

permanent magnets

artificially produced magnets

electromagnets

wire wrapped around an iron core, current in wire creates magnetic field

SI unit of magnetic field strength

Tesla

Traditional unit of magnetic field strength

Gauss

Ampere’s law

a changing electric field induces a magnetic field

For an element to be magnetic it MUST have

an unpaired electron (spin)

Nonmagnetic materials

materials unaffected by magnetic fields (ex: wood/glass)

2 sources of a magnetic field in bar magnet

orbital motion and spin

Ferromagnetic materials

strongly attracted by a magnet and often permanently magnetized (Iron, Nickel, Cobalt)

Every magnet will always have a:

north and south pole

solenoid

coil of wire without a magnetic core

transformers function only with:

alternating current

Domain

a region of ferromagnetic materials where all the dipoles are aligned

sources of inefficiency in a transformer:

copper wire resistance/Joule heating, hysteresis, eddy currents

air core transformer

open core transformer design

autotransformer

closed core transformer

shell type transformer

most effective type of transformer

shell transformer

Farday’s law

a changing magnetic field induces an electrical field

autotransformers use:

self induction

How the strength of a magnetic field is increased

more loops, ferromagnetic core, loops overlapping with other loops

generators convert:

mechanical energy to electrical energy

motors convert:

electrical energy to mechanical energy

Turn ratio greater than 1

Step up transformer

Turns ratio less than 1

step down transformer

transformer law

V2/V1 = N2/N1 = Tr

I1V1=I2V2

I2=I1/Tr

V2/V1 = I1/I2

convection of magnetic field lines

north and south

slip ring

Used in AC generators, produces alternating sinusoidal current

commutator ring

Used in DC motors, produces pulsed direct current

autotransformers use:

1 core, 1 coil, and multiple taps

step up transformer:

increase voltage, decrease current

step down transformer:

decrease voltage, increase current

ferromagnetic materials

iron, nickel, cobalt