Walker Zerr Maxwell (1)

8/3/2019 Walker Zerr Maxwell (1)

1/17

Chapter 14:

Maxwells TheoryBy Katie Zerr and Kristin Walker

Topics that will be covered:

Electromagnetic Theory

Displacement Current

Michelson-Morley ExperimentLIGO

Precursors to Relativity


2/17

James Clerk Maxwell

Born in Edinburgh,Scotland in 1831

Attended EdinburghAcademy, TheUniversity ofEdinburgh, and

Cambridge University Published by the

young age of 14


3/17

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


4/17

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.


5/17

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


6/17

Maxwells Equations

Gausss Law, no monopoles, Amperes Law

and Faradays Law


7/17

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


8/17

Conflict could be resolved by modifying Amperes

Law so that both electric current and displacementcurrent generate the magnetic field:

Displacement Current1st story


9/17

Displacement Current2nd story

For a time dependent electric field, a material mediumwould become polarized, just as a dielectric does

- +

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


10/17

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


11/17

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


12/17

MichelsonMorley Experiment

Swimmers race across the river


13/17

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


14/17

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


15/17

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


16/17

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


17/17

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

Documents

Walker Zerr Maxwell (1)