chapter 24 magnetic fields. magnet a substance that has polarity
TRANSCRIPT
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