It’s what we see…

1. It’s what we see…

2. Light Speed • light around the earth • 300,000,000 m/s • 3 x 108m/s

3. Light Speed • Just over a second from the moon

4. Light Speed • 8 minutes from the sun

5. Light Speed Light Speed • 4.2 years from Alpha Centauri! (second nearest star) • 4.2 years from Alpha Centauri! (second nearest star)

6. Lightyear How far light travels in 1 year • 170, 000 lightyears away • How many years ago did it occur?

7. Plane Mirrors: The Flat Mirrors

8. Plane Mirrors • Incident ray hits the mirror • Reflected ray is the ray that bounces off • The Normal is the perpendicular line from mirror

9. 3 Laws of Reflection • i = r • di to mirror = • do to mirror • Apparent path of light = Actual path of light

10. Draw the Reflected Ray • Draw the normal • Measure the incidentangle • Draw the reflected ray 54° 54°

11. Let practice! Turn to page 15 • Work together to solve #1 and #2

12. #1b. Headlight on a dry road

13. 3 Laws of Reflection • i = r • di to mirror = • do to mirror • Apparent path of light = Actual path of light

14. Reflection • To find an image: extend the reflected ray behind the mirror. • The image is formed where the rays intersect. do di Virtual Image of the nose do= object distance di= image distance

15. Length of Actual Path of light = Length of Apparent path of light mirror Actual path of light? Image Object mirror Apparent path of light

16. Lab part 2: Parallax real screw (behind mirror) • Parallax can be used to find image location • Parallax makes objects appear to move when not in the same place • Try it mirror image of screw

17. Parallax • Move head to the side • If the image and real screw separate, then not at same place • Try it mirror

18. Parallax • If the two move together, they are at same place • Try it mirror

19. Now, to the Lab Part II (pg 11)

20. Common Lab Shortfalls • Use Full Sentences Non-Example: 4.2cm and 4.5 cm. 5% Whatis 4.2cm??? Example of a great response: The distance from the object to the mirror is __ cm and the distance from the mirror to the image is __cm. The percent difference is __% which indicates ___________________.

21. Part 2: Compare using the Percent difference

22. #1. Headlight on a dry road

23. Headlight on a dry road

24. 1. Diffuse Reflectors

25. #3. Find the Object

26. Find the Object Actual path of light Image to eye 14.5 cm Apparent path of light Object 14.5 cm

27. 4. Yourself in a Mirror • Minimum height of mirror?

28. Tip for #4 • Work backwards! Where do the rays need to reach to let everything be seen? Tip for #6 • In order to focus you camera you must know the distance between the camera and the image

29. A man is standing between 2 parallel mirrors looking to the left. Problem 9 How far away from the person are the first three images he sees? mirror object 1.0 m 1.0 m 2.0 m 3.0 m 2.0 m

30. Problem 6 image object 4.5 m 2.0 m 4.5 m 2.0 m

31. Problem 7: But what is the question is asking? θ = incident angle 90° = θ + 25° normal 90° – 25° = θ θ 65° = θ 25° 25° with the surface of the mirror… ?

32. Curved Mirrors

33. Curved Mirror Vocab • C = radius of the sphere the mirror was made from • f= point at which rays converge • F = length of the mirror to f(focal length) • f= C/2 • Concave mirror f C = Focal point Center of curvature

34. Image Types • Virtual images are formed by diverging light rays (example: behind a plane mirror) • Real images are formed by converging light rays Real or Virtual?

35. Vocab Converge Come together from different directions to eventually meet • Come together • Cross • Eventually meet The students will converge in the cafeteria

36. Vocab Diverge Separate and go in different directions • Separate • Grow apart • Turn away Monkeys and Humans diverged from a common ancestor

37. Real vs Virtual Images • Concave Mirror • Image in front • Use a Card to see! • Light rays converge • Image is Real

38. Real vs. Virtual Images • Concave Mirror • Image behind mirror • Appearsto converge • Image is virtual

39. Real Or Virtual ? • Image behindmirror • Appears to converge • Image is virtual

40. Real Or Virtual ? • Image in front of a curved mirror • Appears to diverge • Image is real

41. Let practice! Turn to page 23 • Skip pg 24 • Skip question 3 on page 27 • Normals to the surface have already been drawn as dashed lines.

42. C f Concave Mirrors Incoming Parallel rays reflect: through the focal point!

43. C f Concave Mirrors Rays through (or from) f reflect: parallel!

44. C f Concave Mirrors Rays through C reflect: back through C!

45. C f Convex Mirrors Incoming parallel rays reflect: away from focal point!

46. C f Convex Mirrors Rays towards focal point reflect: parallel! Note: Only the red lines are used to locate the image

47. C f Convex Mirrors Rays towards C reflect: back away from C!

48. Choose easiest paths • (Only need 2) • Use 3rd to “check” The Image is between the Principle axis & the intersection image

49. Finding the Image • Draw ray paths • Identify Characteristics • R = Region • S = Size • O = Orientation • T = Type of Image Beyond C larger inverted Real

50. Now Go Make Your Own! Pages 30-33