Reflection of Light

1. Reflection of Light Electrons in a material respond to light striking the material The energy is either absorbed or reemitted For shiny surfaces like mirrors the reflection obeys a law The angle of reflection equals the angle of incidence

2. Law of Reflection

3. Creating Images

4. Creating Images We trace rays from the object The image formed by the plane mirror is called a virtual image The image is the same distance behind the mirror as the object is in front of it The object and the image are the same size

5. Curved Mirrors The mirror on the right is used as a makeup or shaving mirror since it magnifies

6. Diffuse Reflection When the surface is rough, images are not formed, but the light still reflects

7. Diffuse Reflection Bumps on the surface must be less than about 1/8 the wavelength of light in order to have a smooth surface Big satellite dishes are made of wire mesh and appear smooth to the longer wavelength microwave signals

8. Satellite Dish

9. Satellite Dish

10. Refraction

11. Refraction Recall that when light passes from one material to another, it is bent because the speed of light is different in the two materials Put a stick into water as an example The difference in speed between a material and a vacuum is called index of refraction

12. Index of Refraction

13. Index of Refraction

14. Index of Refraction

15. Refraction When light slows down at a boundary, it bends toward the normal When light speeds up at a boundary, it bends away from the normal The sines of the angles are related to the two indices of refraction

16. Refraction This bending of light can play tricks on our minds

17. Another Trick Light travels faster at higher altitudes because the air is less dense.

18. Dispersion The resonant frequencies where light matches electronic motions tend to be at the high end of the spectrum (violet) The result is that higher frequencies get trapped in electronic motion and then reemitted after a delay High frequencies travel slower than low frequencies

19. Dispersion

20. Dispersion through a Prism

21. Dispersion though a Prism

22. Rainbows

23. Rainbows

24. Rainbows

25. Rainbows

26. Total Internal Reflection At an interface, when light is going from a region of high refractive index (lower speed) to lower index, the light is bent away from the normal If the angle of incidence gets great enough it will be bending away at 90o This is called the critical angle

27. Total Internal Reflection Once the angle of incidence is larger than the critical angle, the light cannot escape the higher index material This means that all the light is reflected from the surface back into the higher index material This is total internal reflection

28. Total Internal Reflection This is used in fiber-optic cables to transmit data signals. The light inside the cable cannot escape so no energy (signal) is lost as it travels.

29. Total Internal Reflection By using high index of refraction glass, we can make prisms that exhibit total internal reflection We can do all sorts of interesting direction changes of light by using these prisms

30. Prisms

31. Prisms

32. Prisms When we study lenses, we will see that we can get greater magnification by increasing the path length between lenses. Here we make binoculars more compact.

33. Prisms

34. Why Love Diamonds?

35. Total Internal Reflection in a Diamond

36. Next time • We complete the Chapter

37. Lenses We use the refractive capability of the air-glass interface to bend light Lenses control the amount of bending to achieve different results Lenses can be either converging or diverging if they are either concave or convex

38. Lenses

39. Lenses

40. Lens Definitions

41. Image Formation Light from every part of the vase strikes every part of the wall. The result is that no clear image is seen.

42. Image Formation The pinhole blocks most of the light so that only light from one place on the vase can hit one place on the wall.

43. Image Formation The lens insures that light from one place on the vase only strikes one place on the wall. But it allows for much more light than the pinhole.

44. Magnifying Glass Note that flower is inside the focal point of the lens

45. Converging Lens When the object is outside the focal point, the image appears on the other side of the lens and is inverted

46. Ray Tracing f f

47. Lens Defects Distortions caused by lenses are called aberrations There are several kinds of aberrations Correct aberrations by using multiple lenses, often of different kinds of glass The two most common kinds are spherical and chromatic

48. Spherical Aberration

49. Chromatic Aberration

50. Wave-Particle Duality This is a shocking topic and a difficult discussion because it shocks your common sense Recall that Young demonstrated the wave nature of light with the two-slit interference pattern that relied on refraction of light at the edges of the slit