Physics Department
PHYS 1P22/92
Sakai
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Ferromagnets and Electromagnets
Electromagnets: macroscopic
current
produces a
magnetic field
Ferromagnets (Fe,Co,Ni,Gd,CrO
2
,SrRuO
3
)
ultimately, atomic currents are the
source of all magnetic fields
Magnetization vector is the magnetic dipole moment per unit volume
spontaneous magnetization
exists below the
Curie Temperature
Magnetic fields of
solenoid (electromagnet) and bar magnet(ferromagnet)
Magnetization can be increased
by heat treatment in a magnetic field
Induced magnetization:
domain alignment
Induced magnetization:
domain alignment
Combining electromagnets and ferromagnets can produce a
very large field
Magnetic
recording head
Magnetic force on a moving charge
operational definition of magnetic field
magnitude:
F=qvB
sinθ
direction:
the right-hand rule #1
: force on + charge
MC:
magnetic force 1
MC:
magnetic force 2
MC:
magnetic force 3
MC:
magnetic force 4
Motion of charged particles in constant magnetic fields
fundamental magnetic force and
the cathode ray tube
lab
experiment
and
observations
electron entering with velocity perpendicular to
magnetic field
MC:
trajectory in B field
MC:
uniform circular motion
MC:
motion in E and B
solar
wind
and
aurora borealis
Ex:
the solar wind
Ex:
alpha particles in B field
scientific applications
velocity selector
existence of isotopes:
mass-spectrometer
electromagnetic method of isotope separation
particle physics
cloud-chamber
conservation of charge and
"pair production"
Magnetic fields produced by electric currents
Oersted's experiment:
Currents produce Magnetic Fields
magnetic field of
a long straight wire
magnetic field of
a loop
magnetic field of
a solenoid
MC:
solenoid
Ex:
Vector Superposition
of Magnetic Fields
MC:
a hairpin current
Magnetic force on an electric current
Magnetic force
on a current
Ex:
magnetic force on a current
MC:
Force between two wires I
Ex:
a flexible loop
Ex:
Net force on a loop
application:
loudspeaker
MC:
Force between two wires II
Ex:
electric train using the Earth's magnetic field
Magnetic Torque and dc electric motors
Magnetic Torque on
a current loop
MC:
torque on a coil
DC electric motor:
split ring commutator
How DC motors work
Electromagnetic induction
magnetic flux
= BA
cos
ø
Ex:
calculating flux
Ex:
magnetic flux
MC:
when is flux decreasing?
Ex:
calculating a change in flux
Faraday's law: voltage induced by a changing magnetic flux
by changing the
magnetic field
by changing the
area
(a shape distortion)
by changing the
angle
: generators
Ex:
a moving rod
Ex:
a shrinking loop
Ex:
changing magnetic field
Ex:
Faraday's law
Lenz's law: induced emf opposes
CHANGE in flux
Induced current creates field that
opposes CHANGE in flux
MC:
Lenz's Law I
MC:
Lenz's law II
MC:
Lenz's law III
MC:
non-conductors/broken circuits
motional emf
Ex:
tethered satellite experiment
applications of electromagnetic induction
ac voltage generators
principle
hydroelectric power generation
Mutual Inductance and Transformers
two coils share the same flux
iron core "concentrates" the field lines
MC:
what can the transformer change?
Ex:
reducing power losses in transmission lines
other applications of electromagnetic induction
Ex:
a moving-coil microphone
Ex:
an electric guitar pick-up coil
Ex:
magnetic tape playback
Ex:
GFI outlets
and
ground-fault detection
Wave Optics
Quantum Physics
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ext.
3412
Email:
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Updated: 04-Mar-2017 11:16