walker zerr maxwell (1)
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Chapter 14:
Maxwells TheoryBy Katie Zerr and Kristin Walker
Topics that will be covered:
Electromagnetic Theory
Displacement Current
Michelson-Morley ExperimentLIGO
Precursors to Relativity
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James Clerk Maxwell
Born in Edinburgh,Scotland in 1831
Attended EdinburghAcademy, TheUniversity ofEdinburgh, and
Cambridge University Published by the
young age of 14
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More on Maxwell
Maxwell differed from his contemporaries
in the nineteenth century
Faraday & Ampere contributed to
Maxwells theories
Much of his important work was
accomplished between the ages of 29 and35
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Aether
Appendix of Chapter 13
When we observe one body acting on another at a distance . . . we
generally inquire whether there is any material connection between the two
bodies . . . we prefer to explain the action by means of these intermediate
connections, rather than to admit the notion of direct action at a distance.
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Maxwells Contributions
Analysis of color perception
An explanation of Saturns rings
Analysis of the theory of fluids and solids
Helped father modern statistical mechanics and the
molecular theory of gases
Theory of ElectromagnetismMaxwells equations
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Maxwells Equations
Gausss Law, no monopoles, Amperes Law
and Faradays Law
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Prior to the Displacement Current
Magnetic field generated solely by electric charge in
motionAmperes Law:
It was also thought (and still is) that electric charge cannotbe created or destroyedthe continuity equation:
Combined, give the result that the amount of
electric charge at any particular place never changes
mathematical contradiction
B = (4/c)j
J + /t = 0
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Conflict could be resolved by modifying Amperes
Law so that both electric current and displacementcurrent generate the magnetic field:
Displacement Current1st story
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Displacement Current2nd story
For a time dependent electric field, a material mediumwould become polarized, just as a dielectric does
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E
For a constantEfield, each pair of charges soon
equilibrates as shown above
If theEfield varies with time, then the charge
configurations are constantly in motiondisplacement
current
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The Final Classical Theory
1865 paper A Dynamical Theory of the
Electromagnetic Field did not discuss
vortices and idle wheels
Classical mechanics was used as model
After consistent defeat, mechanical models
abandoned Electromagnetic theory distinct branch of
physics
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Albert Michelson (1852-1931)
American experimental physicist
Devoted his life to making extremely
accurate measurements of the speed of light Nobel Prize in Physics in 1907 for his
efforts
1887 collaborated with Edward Morley toperform an experiment sensitive enough todetect the earths motion through the aether
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MichelsonMorley Experiment
Swimmers race across the river
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Michelson-Morley Animation
http://galileoandeinstein.physics.virginia.ed
u/more_stuff/flashlets/mmexpt6.htm
http://galileoandeinstein.physics.virginia.edu/more_stuff/flashlets/mmexpt6.htmhttp://galileoandeinstein.physics.virginia.edu/more_stuff/flashlets/mmexpt6.htmhttp://galileoandeinstein.physics.virginia.edu/more_stuff/flashlets/mmexpt6.htmhttp://galileoandeinstein.physics.virginia.edu/more_stuff/flashlets/mmexpt6.htm -
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LIGO
LIGO stands for Laser Interferometer
Gravitational-wave Observatory
Similar apparatus to Michelson-Morley
Run into same problem- trying to block out
high frequency sounds that disrupt results
They hang apparatus while Michelson and
Morley suspended theirs in mercury
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Precursors to Relativity
FitzGerald (1851-1901) could avoid negative
result of Michelson-Morley experiment
Contraction hypothesis was independently
postulated by Hendrik Lorentz
Lorentz manipulated equations and are called
Lorentz transformations today
Lorentz-FitzGerald contraction hypothesis
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Precursors to Relativity (cond)
Poincar postulated that
optical phenomena depend only on the relative motions of
the material bodies He questioned the existence of aether
In 1904 he determined his principle ofrelativity
Lorentz came up with a theory of electronsconsistent with Poincars principle but stillleft room for the aether
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Conclusion
Maxwell provided us with modern physicaland mathematical equations
Many contributions to physics even thoughhis belief in the existence of aether was notvalid
Michelson-Morley experiment proved aether
wrong LIGO today uses similar apparatus and
encounters similar problems
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