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February 2018 Issue, Volume 86, No. 2February 2018 issue of American Journal of Physics

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


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


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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