Chapter 24Magnetic

Fields

Magnet•A substance that

has polarity

Polarity•Charge separation that results in one end being

positive & the other end being negative

Magnets•The ends are called the north & south poles

Magnets•North pole = (+)

•South pole = (-)

Magnets•Opposite poles

attract & like poles repel

Some metals can become temporary

magnets by bringing them close to a strong magnet

Most Permanent magnets are made of ALNICO, an alloy

of Al, Ni, & Co

Very strong, but expensive

permanent magnets are made of neodymium

Magnetic Field•Space where

attractive & repulsive forces act

around a magnet

Magnetic Field•Force fields similar

to gravitational & electric fields

Magnetic Flux•The number of

field lines passing through a surface

Field Strength•Magnetic field

strength is proportional to the flux per unit area

A temporary magnet concentrates

magnetic field lines and is attracted to a permanent magnet

A temporary magnet repels magnetic field lines and is repelled from a

permanent magnet

Electromagnetism•Electric current

generates a magnetic field &

vice versa

Hans Christian Oersted

•First to observe electromagnetic

properties

Electromagnetism•Electric field lines

& magnetic field lines are

perpendicular

First Right-Hand Rule

•Explain •(page 497)

Passing a current through a wire wrapped around a piece of metal

generates a magnetic field

Electromagnet•Magnet generated

by passing a current through a

coiled wire

Second Right-Hand Rule•Explain

•(page 498)

Magnetism at the atomic level•Results from

magnetic fields of electrons

Domain•A group of about 1020 atoms acting

together electromagnetically

Domain•Each domain acts like a dipole (polar

unit)

Magnitism•Magnetism occurs when domains are

aligned

Passing a current through a wire in a

magnetic field exerts a force

Third Right-Hand Rule

•Explain•(page 503)

Magnetic Induction (B)

•Strength of a magnetic field

Magnetic Force•Proportional to

current, field strength, & length

of the wire

Magnetic Force

F = BIL

Magnetic Induction (B)

B = F/IL

Magnetic Induction (B)Measured in

teslas (T)

Tesla (T)

T = N/Am

Galvanometer•Device used to

measure very small currents

Galvanometer•Passing current through

a looped wire in a magnetic field creates a force causing the wire to rotate (page 505)

Galvanometers•Use 3RHR to force a needle to move as

current passes through a MF

Galvanometers•Can measure

currents as small as 10-6 A

Galvanometers•Cannot rotate more

than 180o or more than 90o from parallel to B

Electric Motors•Must be able to

spin 360o

•Explain (page 506)

Electric Motor Force

F = nBIL

F = forcen = # of loops

B = magnetic field strengthI = current

L = length of wire loop

Force on a single charged particle

F = Bqv

F = forceB = Field strength

q = chargev = velocity