Psc CH-24 Magnetic Fields

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Chapter 24
Magnetic
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 RightHand Rule
•Explain
•(page 498)
Magnetism at the
atomic level
•Results from
magnetic fields of
electrons
Domain
•A group of about
20
10 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
-6
10 A
Galvanometers
•Cannot rotate more
o
than 180 or more
o
than 90 from
parallel to B
Electric Motors
•Must be able to
o
spin 360
•Explain (page 506)
Electric Motor
Force
F = nBIL
F = force
n = # of loops
B = magnetic field strength
I = current
L = length of wire loop
Force on a single
charged particle
F = Bqv
F = force
B = Field strength
q = charge
v = velocity
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