brPage 1br USING CDs AND DVDs AS DIFFRACTION GRATINGS brPage 2br Purpose of CDs and DVDs as Diffraction Gratings Activity brPage 3br CDs and DVDs as Diffraction Gratings brPage 4 ID: 18331
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Rama BalachandranChamblee Charter High School Chamblee, GACopyright Georgia Institute of Technology 2009NNIN Document: NNIN 1199 2009 Purpose of CDs and DVDs as Diffraction Gratings ActivityObserve diffraction of light waves through a CD and DVDCDs and DVDs are well know to students so Easy to transition into a discussion about Incorporates nanotechnology by including The rows do not reflect nearly as much light as the in certain directions. Therefore, when white light is reflected from the disc peel off the label and reflecting layers.1: Scratch the label surface of the CD to begin especially with painted labels 3: CD ready to use as transmission tape to peel off the 1: Use a razor blade to the DVD along the edge. polycarbonate layers 4: The transparent piece acts as a transmission Experiment Set-up: Diffraction Pattern screen CD grating Laser central spot Diffraction Images Equationsd (sin) = mm = 0, ±1, ±2, …d = distance between slits = angle of diffraction = wavelength of light m = the order # for the bright fringesTo find measure distance from grating to screen and the first order distance and then by using trigonometry calculate the angle. d x D = tan-1(x/D) Calculations: CD and LaserEquation : dsinxavg = 13.95 cm D = 29.5 cm =angle of diffraction = tan-1 ( x/D) tan-1(13.95/29.5) = 25.3° 10 1.52 m Calculations: DVD and LaserEquation : dsin=mxavg = 42.5 cm D = 20 cm =angle of diffraction = tan-1 ( x/D) tan-1(42.5/20) = 64.8° 10 0.72 m CALCACTUALACTUAL(4.7 GB pattern will agree very well with the spacing Atomic Force MicroscopeAtomic Force Microscopes (AFMs) are devices that measure the surface topography of a The basic principle behind the AFM is based on The forces on the tip can be attractive or AFM http://wills-nanotech.blogspot.com/2006_04_01_archive.html 2 AFM System AFM Images of CD and DVD (unrecorded) Track pitch = 1.57 Track pitch = 0.780 AFM Images CD/DVD (recorded) data encrypted data encrypted Copyright Georgia Institute of Technology 2009NNIN Document: NNIN xxxx