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Maxwell

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Title: Maxwell


1
Chapter 14 Maxwells Theory
By Katie Zerr and Kristin Walker
Topics that will be covered Electromagnetic
Theory Displacement Current Michelson-Morley
Experiment LIGO Precursors to Relativity
2
James Clerk Maxwell
  • Born in Edinburgh, Scotland in 1831
  • Attended Edinburgh Academy, The University of
    Edinburgh, and Cambridge University
  • Published by the young age of 14

3
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 and 35

4
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.

5
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 Electromagnetism Maxwells equations

6
Maxwells Equations
  • Gausss Law, no monopoles, Amperes Law and
    Faradays Law

7
Prior to the Displacement Current
Magnetic field generated solely by electric
charge in motion Amperes Law
?? B (4?/c)j
It was also thought (and still is) that electric
charge cannot be created or destroyed the
continuity equation
?? J ??/?t 0
  • Combined, give the result that the amount of
    electric charge at any particular place never
    changes mathematical contradiction

8
Displacement Current1st story
Conflict could be resolved by modifying Amperes
Law so that both electric current and
displacement current generate the magnetic field
9
Displacement Current 2nd story
For a time dependent electric field, a material
medium would become polarized, just as a
dielectric does
  • For a constant E field, each pair of charges
    soon equilibrates as shown above
  • If the E field varies with time, then the charge
    configurations are constantly in motion
    displacement current

10
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

11
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 to perform
    an experiment sensitive enough to detect the
    earths motion through the aether

12
Michelson Morley Experiment
  • Swimmers race across the river

13
Michelson-Morley Animation
  • http//galileoandeinstein.physics.virginia.edu/mor
    e_stuff/flashlets/mmexpt6.htm

14
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

15
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

16
Precursors to Relativity (cond)
  • Poincaré 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 of relativity
  • Lorentz came up with a theory of electrons
    consistent with Poincarés principle but still
    left room for the aether

17
Conclusion
  • Maxwell provided us with modern physical and
    mathematical equations
  • Many contributions to physics even though his
    belief in the existence of aether was not valid
  • Michelson-Morley experiment proved aether wrong
  • LIGO today uses similar apparatus and encounters
    similar problems
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