February 2018 Issue, Volume 86, No. 2
Rosalind Franklin's X-ray photo of DNA as an undergraduate optical diffraction experiment
Rosalind Franklin's X-ray diffraction patterns of DNA molecules rendered the important clue that DNA has the structure of a double helix. The most famous X-ray photograph, Photo 51, is still printed in most Biology textbooks. We suggest two optical experiments for undergraduates that make this historic achievement comprehensible for students by using macromodels of DNA and visible light to recreate a diffraction pattern similar to Photo 51. In these macromodels, we replace the double helix both mathematically and experimentally with its two-dimensional (flat) projection and explain why this is permissible. Basic optical concepts are used to infer certain well-known characteristics of DNA from the diffraction pattern.
Guest Editorial
Should you consider a community college career? by Andria C. Schwortz. DOI: 10.1119/1.5019345
Papers
Mechanics and statistics of the worm-like chain by Andrew Marantan, and L. Mahadevan. DOI: 10.1119/1.5003376
Rosalind Franklin's X-ray photo of DNA as an undergraduate optical diffraction experiment by J. Thompson, G. Braun, D. Tierney, L. Wessels, and H. Schmitzer. DOI: 10.1119/1.5020051
A toy model for the yield of a tamped fission bomb by B. Cameron Reed. DOI: 10.1119/1.5009102
Positive and negative birefringence of materials in microwave region by Saša Ziherl, Mojca Cepic, and Jurij Bajc. DOI: 10.1119/1.5009237
Oscillations in a half-empty bottle by Andréane Bourges, Amélie Chardac, Aude Caussarieu, Nicolas Plihon, and Nicolas Taberleta. DOI: 10.1119/1.5009664
Self-focusing quantum states by Anthony Allan D. Villanueva. DOI: 10.1119/1.5009921
An optical levitation system for a physics teaching laboratory by Oscar Isaksson, Magnus Karlsteen, Mats Rostedt, and Dag Hanstorp. DOI: 10.1119/1.5007738
Back of the Envelope
Decluttering our thinking with the life-changing magic of twiddle by Sanjoy Mahajan. DOI: 10.1119/1.5020066
Physics Education Research
Analyzing student conceptual understanding of resistor networks using binary, descriptive, and computational questions by Abid H. Mujtaba. DOI: 10.1119/1.5008266
Notes and Discussions
A note on the history of gravity tunnels by Markus Selmke. DOI: 10.1119/1.5002543
Apparatus and Demonstration Notes
A software-based lock-in measurement for student laboratories by David T. Chuss. DOI: 10.1119/1.5011731
BOOKS RECEIVED
American Journal of Physics 86, 160 (2018); https://doi.org/10.1119/1.5019948
The Quantum Labyrinth: How Richard Feynman and John Wheeler Revolutionized Time and Reality by Cameron Reed. DOI: 10.1119/1.5020065
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