CHAPTER 30

1. CHAPTER 30 REFRACTION & LENSES

2. REFRACTION Refraction: is the bending of waves because of the change of speed of a wave when it passes from one medium to another. The greater the difference in the speed of the waves, the greater the bending of the waves.

4. Normal: the line perpendicular to the surface. Incident ray: is the ray of light that strikes the surface. Reflected ray: is the ray of light that bounces off the surface. Refracted ray: is the ray of light that enters the material. Point of Incidence: is the point at which the light strikes the surface.

5. Angle of Incidence: the angle between the incident ray and the normal to the surface. Angle of Reflection: the angle between the reflected ray and the normal to the surface. Angle of Refraction: the angle between the refracted ray and the normal to the surface.

6. When a ray of light travels from a less dense medium to a denser medium; the refracted ray moves towards the normal to the surface. Incident ray air water Refracted ray

7. When a ray of light travels from a denser medium to a less dense medium; the refracted ray moves away from the normal to the surface. air Refracted ray water Incident ray

9. The amount of refraction depends upon: 1. The material through which the light travels. 2. The wavelength of light. The shorter the wavelength, the greater the refraction.

10. Violet light has a smaller wavelength than the other colors in the visible spectrum. Therefore, it is refracted the most.

11. THE LAW OF REFRACTION The greater the value of n, the greater the refraction.

13. Example #1 • The index of refraction of water is 1.33. Calculate the speed of light in water.

15. Example #2 • Find the speed of light in a) ethanol b) quartz c) flint glass.

17. Example #3 • The speed of light in plastic is 2 x 108 m/s. What is the refractive index of the plastic?

19. SNELL’S LAW

20. Example #4 • A light ray of wavelength 589 nm traveling through air strikes a smooth, flat slab of crown glass (refractive index 1.52) at an angle of 300 to the normal. Find the angle of refraction. Incident ray Air=1.00 Glass=1.52 Refracted ray

22. Example #5 • Light in air is incident upon a piece of crown glass at an angle of 450. What is the angle of refraction?

24. Example #6 • A block of unknown material is submerged in water (refractive index is 1.33). Light in the water is incident on the block at an angle of 310. The angle of refraction in the block is 270. What is the index of refraction of the unknown material?

25. Incident ray Water=1.33 unknown Refracted ray

27. Critical Angle the incident angle that causes the incident ray to refract along the boundary between the two surfaces. R = 90° Refracted ray air Incident ray water

30. When the angle of incidence is less than the critical angle; normal refraction takes place. Refracted ray air Incident ray water

31. When the angle of incidence is equal to the critical angle; the refracted ray is on the boundary. Refracted ray air Incident ray water

32. When the angle of incidence is greater than the critical angle; total internal reflection occurs. There is no refracted ray. air Incident ray Reflected ray water

33. TOTAL INTERNAL REFLECTION CONDITIONS • Light is going from a denser medium to a less dense medium. • Light is incident at an angle greater than the critical angle.

34. TOTAL INTERNAL REFLECTION OUTCOMES • There is no refracted ray. • There is only a reflected ray that stays in the denser medium. • Total internal reflection and proper faceting causes diamonds and crystal glass to sparkle brilliantly.

35. EFFECTS OF REFRACTION • Mirages • Lingering daylight after the sun is below the horizon. • An object in water, appears to be closer than it really is. • Spoon appears bent when placed in a glass of water.

36. LENSES • Lenses are curved transparent objects. They form images through refraction of light. They are usually made from plastic or glass. • Two main types of lenses: 1. Convex 2. Concave

39. Convex Lens

40. Convex Lens C F F C

41. Focus or Focal Point: is the point on the principal axis where the parallel rays all come together after passing through the lens. • The distance between the focus and the center of the lens is called the focal length. C C

42. C F F C RULES FOR DRAWING CONVEX LENS RAY DIAGRAMS • Any ray parallel to the optical axis will be refracted through F.

43. C F F C RULES FOR DRAWING CONVEX LENS RAY DIAGRAMS • Any ray passing through F will be refracted parallel to the principal axis.

44. C F F C RULES FOR DRAWING CONVEX LENS RAY DIAGRAMS • Any ray passing through O continues straight through

45. C F F C When object is between F and O • Image is Virtual • Enlarged • And Upright • Used in a magnifying glass

46. C F F C When object is at F • No image is formed • Used in a telescope.

47. C F F C When object is between F and C • Image is enlarged, real, and inverted • Used in optical instruments.

48. C F F C When object is at C • Image is same size, real, and inverted • Used in optical instruments.

49. C F F C When object is beyond C • Image is reduced, real, and inverted • Used in optical instruments.

50. Concave Lens