Wave Nature of Light The Structure of DNA                 Date : July 2016 Author : Mathieu Riopel, Olivier Tardif-Paradis, Alexandre April College : Cégep Garneau Length : About 3 hours Related concept(s) : Young’s experiment, interference, diffraction, structure of DNA     The discovery of the double helix structure of the DNA molecule was one of the major scientific breakthroughs of the 20th century. The story of this discovery reveals the laboratory life, competition and sometimes-difficult human relations that are part and parcel of the research world. In this problem, the students will explore the role played by Rosalind Franklin in this important discovery, which has been long neglected. They will analyse the famous Photograph 51, which was a key component in the development of the double helix model. This photograph, taken using the X-ray diffraction crystallography technique, will allow the students to apply concepts related to physical optics (interference and diffraction). This problem can therefore serve as an introduction to the concepts of interference and diffraction.