1. Major Concepts of Physics PHY102 – Lecture #5 1 2015  Syracuse University Lecture #5 How do we squeeze light through narrow holes? - Diffraction January 28 th Spring 2015 Prof. Liviu Movileanu www.physics.syr.edu/MajorConceptsPhysics2015.html lmovilea@syr.edu Room 211, Physics Bldg., 443-8078 Major Concepts of Physics PHY102

2. Major Concepts of Physics PHY102 – Lecture #5 2 2015  Syracuse University 1. Introduction to diffraction. Huygens’s principle  Big deal! What is the fundamental condition for wave optics (interference, diffraction)? is comparable with a (size of obstacles). 2. Single-slit diffraction  Experimental hypothesis  Single-slit experiment (Experimental evidence)  Diffraction patterns (Interpretation)  Compare interference with diffraction patterns 3. Lecture demonstration (single-slit interference) 4. Diffraction and the resolution of optical instruments 5. Announcements/Homework Lecture objectives

3. Major Concepts of Physics PHY102 – Lecture #5 3 2015  Syracuse University Introduction to Diffraction

4. Major Concepts of Physics PHY102 – Lecture #5 4 2015  Syracuse University Diffraction – The fundamental condition a. Pertinent to geometrical optics -- d >> a. Pertinent to geometrical optics -- d >> b. Pertinent to wave optics --  d d

5. Major Concepts of Physics PHY102 – Lecture #5 5 2015  Syracuse University Introduction to Diffraction b. Circular hole --- Spherical waves c. Rectangular slit --- Cylindrical waves

6. Diffraction patterns Major Concepts of Physics PHY102 – Lecture #5 6 2015  Syracuse University

7. On close examination of the edges, we find: There are alternate regions of darkness and brightness. First known discovery of diffraction: Observations by Francesco Grimaldi, a Jesuit priest, (1618 – 1663). He looked at sunlight entering a darkened room through a tiny hole in a screen. Found: The spot was enlarged, relative to expectations from a particle model of light. He examined the border of the image. Observed: Colored fringes. Grimaldi’s work was the first experimental evidence that light is a wave. Major Concepts of Physics PHY102 – Lecture #5 7 2015  Syracuse University Grimaldi’s work

8. From an experimental point-of-view, there are two signposts of diffraction: When light goes through a small opening, it spreads out like a fan. There is no sharp shadow. Instead, the image is blurred at its edges. The same statements hold, when light encounters an obstacle. Again, there is no sharp shadow. Major Concepts of Physics PHY102 – Lecture #5 8 2015  Syracuse University Diffraction: a brief review

9. Major Concepts of Physics PHY102 – Lecture #5 9 2015  Syracuse University

10. Major Concepts of Physics PHY102 – Lecture #5 10 2015  Syracuse University

11. Major Concepts of Physics PHY102 – Lecture #5 11 2015  Syracuse UniversityAnnouncement

12. Major Concepts of Physics PHY102 – Lecture #5 12 2015  Syracuse University (a/2)sin  =m( /2) first minimum

13. Major Concepts of Physics PHY102 – Lecture #5 13 2015  Syracuse University

14. Major Concepts of Physics PHY102 – Lecture #52015  Syracuse University Rayleigh’s criterion 14

15. Major Concepts of Physics PHY102 – Lecture #5 15 2015  Syracuse University Observation of diffraction

16. Major Concepts of Physics PHY102 – Lecture #5 16 2015  Syracuse University Example 25.8 – Continuation

17. Major Concepts of Physics PHY102 – Lecture #5 17 2015  Syracuse University Example 25.8 – Continuation

18. Major Concepts of Physics PHY102 – Lecture #5 18 2015  Syracuse University Example 25.9

19. Major Concepts of Physics PHY102 – Lecture #5 19 2015  Syracuse University

20. Major Concepts of Physics PHY102 – Lecture #5 20 2015  Syracuse University Applications of diffraction: X-ray diffraction Rosalind Frankin (1953) James Watson and Francis Crick

21. Major Concepts of Physics PHY102 – Lecture #5 21 2015  Syracuse University 1. Reading 1. Reading: Chapter 25 th, Sections 25.6, 25.7, 25.8, 25.9 (pages 962-971). Conceptual examples 25.7, 25.8 and 25.9 2. Homework 2. Homework for the next week (on paper): Please pick up the print outs today (or see the class website). The homework #2 is due on next week’s workshop. 3. Do you want to be challenged? 3. Do you want to be challenged? More MCAT preps? Problems 25.7 Diffraction by a single slit Problems 25.8 Diffraction and the resolution of optical instruments 4. This week’s lab: Interference Announcements