The Disappearing Beaker The simple mathematics you can use to motivate one of the best and easiest physics demonstrations ever Hope Concannon The North Carolina School of Science and Mathematics 1219 Broad Street Durham, NC 27705 email: [email protected] We have all experienced refraction when we notice the apparent bending of an object when it is dipped in water. What is really going on here? http://eyestravel.eu/wp-content/uploads/2013/03/refraction.jpg http://www.opticampus.com/nature_light/images/Slide13.GIF http://www.patana.ac.th/secondary/science/anrophysics/ntopic4/images/car_refraction.jpg The Law of Refraction Notice the tie between this equation and the Law of Sines! Some implications and activities using the Law of Refraction Light bends at a boundary between two materials with different optical densities. http://www.gareyscience.com/ana22/waves_online_lesson/refraction-pencil-all.jpg If you want a quick lab, students can measure the angle of incidence and angle of refraction and verify that the Law of Refraction describes what they see. http://farm5.static.flickr.com/4129/5079318821_8ac68e77f5.jpg Total Internal Reflection Think about the direction light bends when traveling from water into air. What happens when the exiting ray travels along the surface of the water? What happens at even steeper incident angles? http://theboard.byu.edu/media/attached_files/r_96768/Total-Internal-Reflection.gif Is there an incident angle 1 where the light will exit along the boundary surface (2 = 90°)? sin 1 1 = sin 2 2 becomes sin 1 = 1 2 This has a solution only if light is speeding up at the boundary (so 1 < 2 and 1 2 < 1)! Optical Fibers Where did the pipette and test tube go? http://gr5.org/index_of_refraction/babywess.jpg https://webspace.utexas.edu/cokerwr/www/index.html/tubeinoil.JPG A full handout of this talk will be available on the web after this conference at http://courses.ncssm.edu/talks/conferences/ Thank you for coming!