Discussion of dispersion and rainbows. Also some cool photos of blackbody and fluorescent spectra from Tom Decaro and Analisa Goodman as part of the homework question.

2. HW Question Tom Decaro—Sunlight reflections through a diffraction grating

3. Tom Decaro—Sunlight reflections through a diffraction grating

4. Tom Decaro -- Fluorescent lights through a diffraction grating

5. Analisa Goodman—Fluorescent lights through a diffraction grating

7. Conservation of energy in lighting Electrical Energy Heat flow Invisible photons Visible photons In winter, these are beneficial for heating the room Lighting Efficiency Visible photons Electrical Energy

8. First off, let’s experiment with refraction Key Concept Compared with speed in a vacuum (300 million meters per second) Light travels SLOWER inside matter

12. TIR is a key for fiber optic communication Air glass http://www.fiberoptic-connectors.com/images/reflection.gif

13. TIR enables a special surface microscopy technique Air glass “ Evanescent” Wave Excite fluorescence in cell with evanescent wave www.olympusamerica.com Red = TIRF Green = regular

18. Demos Prisms Acrylic sphere rainbow http://www.youtube.com/watch?v=rQukmSPctks&feature=related

19. Rainbows are the result of dispersion inside spherical raindrops (close to 1 millimeter in size) NOT THIS SHAPE! Higher frequencies Refract MORE Each raindrop emits it’s own “fan” For a given raindrop, your eye will only see rays of particular angle. http://www.atoptics.co.uk/ http://www.tpwd.state.tx.us

20. These special angles form a 3-D cone… which you see as a portion of a CIRCLE “ Primary rainbow” = one reflection http://www.atoptics.co.uk/rainbows/primrays.htm

21. Two reflections allow light to go in other directions And produce the secondary rainbow Two reflections http://www.atoptics.co.uk/rainbows/orders.htm

24. Rainbow colors are not exactly the same as through a prism (or diffraction grating)…what differences do you notice? Rainbow Prism Diffraction Grating

25. Rainbows differ from regular prism spectra, because colors overlap Website demo http://www.sundog.clara.co.uk/rainbows/primrays.htm

26. Why is it dark between the primary and secondary rainbow? http://www.atoptics.co.uk/rainbows/adband.htm Alexander’s dark band Spectacular rainbow, late afternoon Sweden, 1999. http://www.atoptics.co.uk/index.htm

27. Reflection Bows

28. Clicker…which bow is formed by the reflection? A B

29. Go to this website for many fascinating atmospheric phenomena! http://www.atoptics.co.uk/