1. 1 Reflection and Mirrors Chapter 17

2. 2 The Law of Reflection When light strikes a surface it is reflected. The light ray striking the surface is called the incident ray. A normal (perpendicular) line is then drawn at the point where the light strikes the surface. The angle between the incident ray and the normal is called the angle of incidence. The light is then reflected so that the angle of incidence is equal to the angle of reflection. The angle of reflection is the angle between the normal and the reflected light ray.

3. 3 Incident Ray Angle of Incidence Reflected Ray Angle of Reflection Mirror Normal

4. 4 The incident ray, normal, and reflected ray are all in the same plane.

5. 5 Regular reflection occurs when light is reflected from a smooth surface. When parallel light rays strike a smooth surface they are reflected and will still be parallel to each other.

6. 6 Diffuse reflection occurs when light is reflected from a rough surface. The word rough is a relative term. The surface is rough at a microscopic level. For example, an egg is a rough surface. When parallel light rays strike a rough surface, the light rays are reflected in all directions according to the law of reflection.

7. 7 Light reflected from the surface of a painted wall would be an example of ____ reflection. A. Regular B. Diffuse

8. 8 Concave mirrors are made from a section of a sphere whose inner surface was reflective. Concave mirrors are also known as converging mirrors since they bring light rays to a focus. They are typically found as magnifying mirrors Convex mirrors are made from a section of a sphere whose outer surface was reflective. Convex mirrors are also known as diverging mirrors since they spread out light rays. They are typically found as store security mirrors. Types of Mirrors Convex Concave

9. 9 Plane Mirrors have a flat surface. The mirror hanging on the wall in your bathroom is a plane mirror.

10. 10 Real images are images that form where light rays actually cross. In the case of mirrors, that means they form on the same side of the mirror as the object since light can not pass through a mirror. Real images are always inverted (flipped upside down). Virtual images are images that form where light rays appear to have crossed. In the case of mirrors, that means they form behind the mirror. Virtual images are always upright.

11. 11 What type of image is shown above? –A. Real –B. Virtual Original image

12. 12 Plane Mirror In a plane mirror the object is the same size, upright, and the same distance behind the mirror as the object is in front of the mirror.

13. 13 Images in a plane mirror are also reversed left to right.

14. 14 What type of mirror created this image? A.Plane B.Convex C.Concave OriginalImage

15. 15 The center of curvature also known as radius of curvature (C) of a curved mirror is located at the center of the sphere from which it was made. The principle axis is a line that passes through both the center of curvature (C) and the focal point (f) and intersects the mirror at a right angle. C = 2f The focal point (f) is located halfway between the mirror’s surface and the center of curvature. Curved Mirrors

16. 16 A concave mirror has a radius of curvature of 15 cm. What is the focal length of this mirror? A. 15 cm B. 30 cm C. 7.5 cm

17. 17 fC Principle Axis Concave Mirrors Light source Convex Mirrors fC Principle Axis Light source

18. 18 Rules for Locating Reflected Images 1. Light rays that travel through the center of curvature (C) strike the mirror and are reflected back along the same path. 2. Light rays that travel parallel to the principle axis, strike the mirror, and are reflected back through the focal point (f). 3. Light rays that travel through the focal point (f), strike the mirror, and are reflected back parallel to the principle axis.

19. 19 All three of these light rays will intersect at the same point if they are drawn carefully. However, the image can be located by finding the intersection of any two of these light rays.

20. 20 Locating images in concave mirrors

21. 21 Concave Mirror with the Object located beyond C

22. 22 Light rays that travel through the center of curvature (C) hit the mirror and are reflected back along the same path. Concave Mirror Object beyond C

23. 23 Light rays that travel parallel to the principle axis, strike the mirror, and are reflected back through the focal point (f). Concave Mirror Object beyond C

24. 24 Light rays that travel through the focal point (f), strike the mirror, and are reflected back parallel to the principle axis. Concave Mirror Object beyond C

25. 25 Concave Mirror Object beyond C Image: Real Inverted Smaller Between f and C The image is located where the reflected light rays intersect

26. 26 Concave Mirror with the Object located at C

27. 27 Concave Mirror Object at C Light rays that travel parallel to the principle axis, strike the mirror, and are reflected back through the focal point (f).

28. 28 Concave Mirror Object at C Light rays that travel through the focal point (f), strike the mirror, and are reflected back parallel to the principle axis.

29. 29 Concave Mirror Object at C Image: Real Inverted Same Size At C The image is located where the reflected light rays intersect

30. 30 Concave Mirror with the Object located between f and C

31. 31 Concave Mirror Object between f and C Light rays that travel through the center of curvature (C) hit the mirror and are reflected back along the same path. fC

32. 32 Concave Mirror Object between f and C Light rays that travel parallel to the principle axis, strike the mirror, and are reflected back through the focal point (f). fC

33. 33 Concave Mirror Object between f and C Light rays that travel through the focal point (f), strike the mirror, and are reflected back parallel to the principle axis. fC

34. 34 Concave Mirror Object between f and C Image: Real Inverted Larger Beyond C The image is located where the reflected light rays intersect fC

35. 35 Concave Mirror with the Object located at f

36. 36 Concave Mirror Object at f Light rays that pass through the center of curvature hit the mirror and are reflected back along the same path.

37. 37 Concave Mirror Object at f Light rays that travel parallel to the principle axis, strike the mirror, and are reflected back through the focal point (f).

38. 38 Concave Mirror Object at f No image is formed. All reflected light rays are parallel and do not cross

39. 39 Concave Mirror with the Object located between f and the mirror

40. 40 Concave Mirror Object between f and the mirror Light rays that travel through the center of curvature (C) hit the mirror and are reflected back along the same path.

41. 41 Concave Mirror Object between f and the mirror Light rays that travel through the focal point (f), strike the mirror, and are reflected back parallel to the principle axis.

42. 42 Light rays that travel parallel to the principle axis, strike the mirror, and are reflected back through the focal point (f). Concave Mirror Object between f and the mirror

43. 43 Concave Mirror Object between f and the mirror Image: Virtual Upright Larger Further away The image is located where the reflected light rays intersect

44. 44 Locating images in convex mirrors

45. 45 Convex Mirror with the Object located anywhere in front of the mirror

46. 46 Light rays that travel through the center of curvature (C) hit the mirror and are reflected back along the same path. Convex Mirror Object located anywhere fC

47. 47 Light rays that travel parallel to the principle axis, strike the mirror, and are reflected back through the focal point (f). Convex Mirror Object located anywhere fC

48. 48 Light rays that travel through (toward) the focal point (f), strike the mirror, and are reflected back parallel to the principle axis. Convex Mirror Object located anywhere fC

49. 49 Convex Mirror Object located anywhere Image: Virtual Upright Smaller Behind mirror, inside f The image is located where the reflected light rays intersect fC

50. 50 What type of mirror could have created the image shown above? –A. Plane –B. Concave –C. Convex Original Image

51. 51 Where would the object need to be placed to create this image? –A. At C –B. Between f and C –C. Beyond C –D. Between f and the mirror Original image

52. 52 Where would this image form? –A. At C –B. Between f and C –C. Beyond C –D. Between f and the mirror Original image

53. 53 Mirror Equation (1/f) = (1/d o ) + (1/d i ) f = focal length d o = object distance d i = image distance

54. 54 Mirror Magnification Equation M = -(d i / d o ) = (h i / h o ) M = magnification d i = image distance d o = object distance h i = image height h o = object height

55. 55 Mirror Sign Conventions F + for Concave Mirrors - for Convex Mirrors d i + for images in front of the mirror - for images behind the mirror d o + always h i + if upright image - if inverted image h o + always M + if virtual - if real image Magnitude of magnification <1 if smaller =1 if same size >1 if larger

56. 56 If the focus of a convex mirror is 60 cm from the mirror, what is the radius of curvature? A. 120 cm B. -120 cm C. 30 cm D. -30 cm

57. 57 A concave mirror of radius 60 cm is placed so that a luminous object is 35 cm in front of the mirror. Where does the image form? A. 0.0048 cm B. 210 cm C. -0.012 cm D. -84 cm

58. 58 A man 2 m tall stands 10 m in front of a convex mirror which has a radius of curvature of 5 m. How tall is the image? A. 0.4 m B. -0.7 m C. 0.7 m D. 2 m