Lect32_[Compatibility_Mode]

Lect32_[Compatibility_Mode] - Physics 344 Foundations of...

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Physics 344 Foundations of 21 st Century Physics: Relativity, Quantum Mechanics and heir Applications Their Applications Instructor: Dr. Mark Haugan Office: PHYS 282 [email protected] TA: Dan Hartzler Office: PHYS 7 [email protected] Grader: Shuo Liu Office: PHYS 283 [email protected] Office Hours: If you have questions, just email us to make an ppointment. e enjoy talking about physics! appointment. We enjoy talking about physics! Notices: Since we have time for only one more problem set before Thanksgiving, I will handout Problem Set 11 next Monday. It will be due a week from then at our last class before Thanksgiving. gg Midterm II at 8:00pm, Thursday, December 2 in MSEE B012
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ecitation Recap Recitation Recap Yesterday we discussed the special case of x-ray diffraction by a crystal with angle of cidence equal to the diffracted angles θθ incidence equal to the diffracted angles. We say diffraction rather than reflection because the x-ray wavelength is comparable to the spacing between atoms, so, a continuum model of the 12 crystal matter is inadequate. Each atom scatters x-rays in many directions and interference between the scattered waves determines in which directions the x-ray intensity is strong. s we saw in the case of 2- ource interference it is useful to think in terms of As we saw in the case of 2 source interference, it is useful to think in terms of ray paths and wave phase to sort out the conditions for constructive and destructive interference. the figure above, parts of the wave scattered by atoms 1 and 2 that will In the figure above, parts of the wave scattered by atoms 1 and 2 that will interfere in the direction shown are scattered at different times. However, because the extra distance s 2 that an x-ray wavefront reaching atom 2 before being scattered is equal to the extra distance s 1 a wavefront scattered by atom 1 travels before superposing on the wave scattered by 2, the interference between these waves is always constructive in the special case with the angle of diffraction equal to the angle of incidence.
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Question 1. Strong diffracted x-ray intensity is possible at other angles. In those cases the extra distances s 1 and s 2 are not equal. What is the condition for constructive interference in uch cases for x ys with wavelength such cases for x-rays with wavelength λ ? A) s 1 > s 2 B) s 1 < s 2 C) | s 1 - s 2 | = n λ for n an odd integer D) | s 1 - s 2 | = n λ for n an integer E) | s 1 - s 2 | = n λ /2 for n an odd integer When diffracted from a single crystal an x-ray beam roduces a spot on a film detector like these ones. produces a spot on a film detector like these ones. If we rotate the crystal around an axis parallel to the incident x-ray beam, each such spot is y, p swept into a ring on a film detector like these ones.
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This note was uploaded on 11/26/2010 for the course PHYS 344 taught by Professor Garfinkel during the Spring '08 term at Purdue.

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Lect32_[Compatibility_Mode] - Physics 344 Foundations of...

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