Physics 344Foundations of 21stCentury Physics: Relativity, Quantum Mechanics and Their ApplicationsTheir 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 appointment.We enjoy talking about physics!appointment. 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. Midterm II at 8:00pm, Thursday, December 2 in MSEE B012
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Recitation RecapYesterday we discussed the special case of x-ray diffraction by a crystal with angle of incidence equal to the diffracted anglesθθincidence 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 t lttiidtEhtttiditi12crystal 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. As we saw in the case of 2-source interference it is useful to think in terms ofAs 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. In the figure above, parts of the wave scattered by atoms 1 and 2 that willIn 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 s2that an x-ray wavefront reaching atom 2 before being scattered is equal to the extra distance s1a wavefront scattered by t1 tlb fithttd b2 thi tfatom 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.