History 181B - Class 6

History 181B: Modern Physics

Class 6 (2/3/03)
Electromagnetism

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Outline

Field physics
    What is a field?
    Maxwell on Faraday, and methodology
    Other analogies for E&M

Physical optics: the nature of light
    Huygens and Newton
    Corpuscular theories
    Interference and waves
    Waves in a medium

Connecting optics to electromagnetism
    Empirical unification
    The electromagnetic-luminiferous aether
    Maxwell's new analogy

Names and terms

Primary	Secondary
lines of force field James Clerk Maxwell (1831-1879) "On Faraday's Lines of Force" (1855) physical analogy (or model) luminiferous aether longitudinal, transverse interference vortex, vortex atom "On Physical Lines of Force" (1861-1862)	George Green (1793-1841) Carl-Friedrich Gauss (1777-1855) Christian Huygens (1629-1695) Thomas Young (1733-1829) Augustin Fresnel (1788-1827) polarization magnetooptic rotation (Faraday effect)

Assignment

James Clerk Maxwell, selection from "On Faraday's Lines of Force" (1855), in The Scientific Papers of James Clerk Maxwell, ed. W. D. Niven (Cambridge: Cambridge University Press, 1890; New York: Dover, 1952), v. 1, 155-159; letter to Thomson, 10 December 1861, in Origins of Clerk Maxwell's Electric Ideas as Described in Familiar Letters to William Thomson, ed. Sir Joseph Larmor (Cambridge: Cambridge University Press, 1937), 34-35; selection from "On Physical Lines of Force" (1861), Scientific Papers, v. 1, 488-489.

    What did Maxwell mean by a physical analogy? What were its advantages relative to purely mathematical formulas on the one hand, to physical theories on the other?
    Why did he believe a physical analogy was appropriate at this stage of his science?
    The essential physical analogy in the first paper likens Faraday's lines of force to the flow of an incompressible fluid. How did Maxwell flesh out the analogy?
    What startling result does Maxwell obtain on p. 35 of his letter to Thomson?
    Extra: This final intuition is explored further in the article that follows (of which you are reading only the end). Try mapping Maxwell's specifications on p. 34 of his letter onto Fig. 2 of his article.

AND start reading McCormmach, Night Thoughts of a Classical Physicist