1. Light Physics 100 Chapt 17

2. Galileo’s attempt to measure the speed of light

3. Galilean moons

4. Ole Roemer

5. Eclipses of Jupiter’s moons Sun Earth Jupiter Io Light from eclipse #1 travels this far

6. Eclipses of Jupiter’s moons Sun Jupiter Io Light from the next eclipse has to travel this much farther Earth Measured time between eclipses is a little longer than actual time

7. 6 months later Sun E arth Jupiter Io Light from eclipse #1 travels this far

8. 6 months + later Sun Jupiter Io Light from the next eclipse travels a distance that is this much shorter Earth Measured time between eclipses is a little shorter than actual time

9. Reflections

10. Reflection from a flat surface angle of incidence = angle of reflection

11. Image

12. Wall mirror left hand right hand

13. Speed of light is slower Refraction Speed of light is faster  air  h2o

14. Refraction

15. where should you aim? At the fish? Above it? Below it?

16. answer

17. “Broken stick”

18. Broken pencil

19. Dispersion

20. Dispersion in a water droplet

21. rainbow Sun

22. Wave nature of light

23. Interference from two wave sources

24. Light thru a single narrow slit central bright stripe wider than shadow of the slit!

25. Light thru a narrower single slit central bright stripe gets wider!

26. Single slit “diffraction pattern” “Intensity pattern”

27. Light thru two narrow closely spaced slits Diffraction pattern with dark stripes

28. Two slit interference pattern “Intensity pattern”

29. Bright stripes

30. Dark stripes

31. Two slits

32. Single slit diffraction

33. Single-slit interference

34. Any aperture produces interference

35. Two adjacent holes

36. Move holes closer together

37. Photo using IR light

38. Human vision Visible light wavelengths 0.75x10 -6 m0.4x10 -6 m Human hair: Thickness = ~100 x 10 -6 m (100  m) Red blood cell: diameter = ~5 x 10 -6 m (5  m) hemoglobin molecule: ~0.01 x 10 -6 m (0.01  m) No way! (albeit with a microscope) OK!

39. Rule of thumb To view an object using a wave, the wavelength of the wave must be shorter than the dimensions of the features that you want to examine.

40. “proof” that light is a wave With 2 slits open no light goes here Block off one slit Now light can go here

41. Somehow the light going through one slit knows whether or not the other slit is open or closed This is possible for a wave, which is extended in space, but not for a localized particle

42. Doppler effect applies to light also

43. Red-shift --- Blue shift