Re: [ccp4bb]: electromagnetic wave

[Eaton Lattman]

Imagine an EM wave traveling in the x direction with E pointing along y and B pointing along z.  Erect a tiny rectangle in the x-y plane of width dx.  Apply Faraday’s Law of Induction to relate the magnetic flux through the rectangle to the integral of E around is perimeter.  One finds that   ∂E/∂x = - ∂B/∂t   So it is the magnitude of the derivatives that are equal.  And this is an agreement with the functional form   B = Bm•sin(kx – wt)      and E = Em•sin(kx-wt)   Which corresponds to the drawing int eh Eisenberg book. Ed Eaton E. Lattman Mail to: Dean of Research and Graduate Education Johns Hopkins University Professor of Biophysics 3400 North Charles Street Krieger School of Arts and Sciences Mergenthaler 237 Johns Hopkins University Baltimore, MD 21218 410 516-8215 voice 410 516-4100 fax On Jul 6, 2006, at 2:55 PM, Bernhard Rupp wrote: ***  For details on how to be removed from this list visit the  *** ***          CCP4 home page http://www.ccp4.ac.uk         *** Dear All: A question for the theory-erudite: X-rays are electromagnetic radiation. Most of the time in crystallography we concern ourselves only with the electric field vector, which rings the electrons etc etc. ok.   Interactions between dielectric matter and magnetic field are generally six orders of magniture smaller than for electrostatic interactions (so much for the magnetic wonder water treatments and crystallization secrets). However, for the self-propagation of the photon package, the magnetic field vector, perpendicular to the electric field, is equally important.  I have seen a drawing - I recall in Eisenberg's Physical Chemistry, that shows Electric and magnetic field vector at the maximum at the same point. If I look at the Maxwell equations, it appears however, that at the maximal change of H, induced E is largest, and at maximal change of E, the induced H. So should not H peak, when E goes though zero? This would create some 'selfinduction' or 'propagation'. Obviously something is wrong with my picture. Can anyone shed light on the phase relation between H and E in a wave packet? I did not find any  other drawing or explicit explanation in any of my older (German) physics books, and I was never really hot on electrodynamics. Any references would be welcome.  Cheers, br