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PHY122_L21PostingAfterLecture

PHY122_L21PostingAfterLecture - PHY122 – Physics for the...

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Unformatted text preview: PHY122 – Physics for the Life Sciences II Lecture 21 Quantum Physics, part 1 Did anyone else see Brian Greene’s NOVA program “Quantum Leap” (the 3 rd of a 4-part series called “The Fabric of the Cosmos”) last night on PBS/Channel 13? Highly recommended ! See it at http://video.pbs.org/video/2167398185 HW 12 due Sunday, 20 Nov. at 8 pm Note: Clicker Channel 21 11/17/2011 Lecture 21 1 11/03/2011 Lecture 17 2 X-Ray Diffraction X-ray diffraction is a crucial research tool for physics, chemistry, material science, and ... X-ray diffraction patterns from a crystal illuminated by a (monochromatic) x-ray beam allow us to determine inter-atomic and inter- molecular distances and deduce the details of the molecular structure… X-ray beam incident on a crystal plane: constructive interference from adjacent lattice sites when θ inc = θ refl = θ • x-rays are penetrating; constructive interference from underlying crystal “planes” when 2 d cos θ = m λ • x-ray diffraction spots here for DNA Rosalind Franklin, 1953 Note: We follow the textbook (see Fig. 28.4, p. 924) and use angles defined with respect to the normal to the plane. BEWARE: all “x-ray people” use the angle “to the plane” by custom!!! In HW 12, use the “angle to the normal” as we do here. 2 d cos θ = m λ Electricity and Magnetism Maxwell’s Electromagnetic Waves: • Important consequence: one can calculate the absolute velocity of electromagnetic waves “in terms of electrical quantities” (used for, e.g., capacitors and inductors): From Maxwell (1864): “ This velocity is so nearly that of light, that it seems we have strong reasons to conclude that light itself (including radiant heat, and other radiations if any) is an electromagnetic disturbance in the form of waves propagated through the electromagnetic field according to electromagnetic laws.” 11/17/2011 Lecture 21 3 1 v c μ ε = ≡ From Maxwell to Einstein • Finished “Diploma” (like MS) in 1901 and Ph.D. in 1905. • While working in Swiss Patent Office (1901-8) he also worked on his “Habilitation” to be able to seek a Professorship at a German university. • His “annus mirabilis” = “miracle year” was 1905. He published 4 monumental physics papers that helped to bridge “classical physics” to the very small: atoms and molecules (quantum physics) and to the very large: Special (later General) Relativity and the “cosmos” Read the biography of Einstein “Subtle is the Lord” by Abraham Pais 11/17/2011 Lecture 21 4 Albert Einstein (1879-1955). Nobel Prize: 1921 mainly for his theoretical (quantal) explanation of the “photoelectric effect” Einstein’s Revolution #1 He takes Maxwell at his word: speed of light in vacuum This is i n d e p e n d e n t of any frame of reference!...
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PHY122_L21PostingAfterLecture - PHY122 – Physics for the...

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