We derive the Einstein relations, which connect the conductivity with the diffusion coefficient. This is far more exciting than it sounds, because it's a consequence of the far-reaching fluctuation-dissipation theorem. Another instance of this theorem happens with Brownian motion, and the applet we used in class can be found athttp://galileo.phys.virginia.edu/classes/109N/more_stuff/Applets/brownian/brownian.htmlWe also derive the continuity equations in a semiconductor, and see how fast they can screen a stray charge that may be produced by, say, thermal fluctuations. We highlight 2 applications of semiconductors: LED's and solar cells.We discuss a bit the impending energy challenge, referring to a talk by Nobel Laureate Richard Smalley. Sadly, he has passed away.Lecture Audio

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