PHY132_L25 - Classical Physics II Classical Physics II...

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lassical Physics II Classical Physics II PHY132 Lecture 25 Electromagnetic Radiation Lecture 25 1 04/07/2010
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Maxwell’s Equations Four equations together completely describe all the material covered so far (i.e. all of electromagnetism); they are called Maxwell’s Equations: on the direct sources of E and B: – Gauss’ Law for E : (our workhorse for the E -field) – Gauss’ Law for B : (no magnetic monopoles) encl 0 dQ  EA 0 d BA on the deep connections between E and B : – Ampere’s Law: (with Maxwell’s i D ) araday’s Law ith Lenz’ Law)   0C h a r g e 0 encl. E di d d t  B l d d t – Faraday s Law: (with Lenz Law) • note: symmetry would be perfect if magnetic mono poles and currents of monopoles existed … Maxwell showed that these 4 laws predict the existence of ELECTRO- AGNETIC waves propagating through vacuum B dd   E l E MAGNETIC waves, propagating through vacuum, at the speed of light c= 1/ ( ε 0 μ 0 ) – This was revolutionary at the time: waves were only thought to Lecture 25 2 propagate in a MEDIUM – Maxwell postulated the AETHER as the medium for EM waves… with very weird properties … 04/07/2010
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Thinking a bit about waves… • Consider a charge which is “shaking back-and-forth”. • Such a charge is being continuously accelerated… he ield lines of a static charge are thus “shaken back • The E -field lines of a static charge are thus shaken back and forth” as well and the field wiggles propagate outwards with the speed of light; • The moving charge also creates magnetic field circles, which oscillate in strength: me arying ield is created at any point • a time-varying magnetic field is created at any point, perpendicularto the local E -field.
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This note was uploaded on 04/14/2010 for the course PHY 132 taught by Professor Rijssenbeek during the Spring '04 term at SUNY Stony Brook.

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PHY132_L25 - Classical Physics II Classical Physics II...

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