The Role of Light to Sight

Transcription

1 Reflection

2 The Role of Light to Sight The visual ability of humans and other animals is the result of the complex interaction of light, eyes and brain. Absence of Light Darkness.

3 Luminous objects are objects that generate their own light. Illuminated objects are objects that are capable of reflecting light to our eyes.

4 The Line of Sight In order to view an object, you must sight along a line at that object; and when you do light will come from that object to your eye along the line of sight.

5 Reflection Object distance = Image distance

6 Incident ray - The light ray approaching the mirror. Reflected ray - The light ray then reflects off the mirror and travels to your eye. To view the image of an object in a mirror, you must sight along a line at the image. One of the many rays of light from the object will approach the mirror and reflect along your line of sight to your eye. The distance from the mirror to the object (known as the object distance) is equal to the distance from the mirror to the image (known as the image distance).

7 The Law of Reflection

8 Reflection and the Locating of Images Image visible Image not visible

9 The Law of Reflection is Always Observed(regardless of the orientation of the surface) Microscopic view of paper

10 Specular vs. Diffuse Reflection

11 Photograph of Mount Moran in the Grand Teton National Park in Wyoming - taken by Becky Henderson

12 Why is an Image Formed?

13 Apparent Left-Right Image Reversal But, objects are not inverted!

14 Ray Diagrams A ray diagram is a diagram that traces the path that light takes in order for a person to view a point on the image of an object Drawing Ray Diagrams 1. Draw the image of the object.

15 2. Pick one extreme on the image of the object and draw the reflected ray that will travel to the eye as it sights at this point.

16 3. Draw the incident ray for light traveling from the corresponding extreme on the object to the mirror.

17 4. Repeat steps 2 and 3 for all other extremities on the object.

18 Practice drawing Ray Diagrams.

19 Solution to the Practice Problem

20 Uses of Ray Diagrams

21 What Portion of a Mirror is Required? To view an image of yourself in a plane mirror, you will need an amount of mirror equal to one-half of your height.

22 What is the Effect of Varying Object Distance? The two ray diagrams above demonstrate that the distance that a person stands from the mirror will notaffect the amount of mirror that the person needs to see their image.

23 Right Angle Mirrors Two plane mirrors placed at an right angle mirrors produce three images!

24 Investigating the Three Images

25 Primary Images - Image 1 & 2 Right & left reversal is observed. Secondary images - Image 3 There is no right & left reversal Image distance = Object distance Ray Diagram

26 Other Multiple Mirror Systems With two plane mirrors oriented at a nearly 50 degree angle to one another, six different images are formed of an object.

27 A Pair of Parallel Mirrors

28

29 The Anatomy of a Curved Mirror We will study curved mirrors that have a spherical shape. Such mirrors are called spherical mirrors. Concave Mirrors and Convex Mirrors.

30 Vocabulary: Principal Axis Center of Curvature C Vertex A Focal Point F Radius of Curvature R Focal Length f f = ½ R Concave mirrors

31 Incident light rays that travel parallel to the principal axis towards the mirror will meet after reflection at the focal point. Dish antennas Satellite receivers

32 Reflection of Light and Image Formation Light always follows the Law of Reflection, whether the reflection occurs off a curved surface or off a flat surface. For a concave mirror, the normal at the point of incidence on the mirror surface is a line that extends through the center of curvature. Concave mirrors produce Real and Virtual images.

33 What is an Image? How is it Formed? At the point where the light from the object converges, a replica, likeness or reproduction of the actual object is created. This replica is known as the image.

34

35 Two Rules of Reflection for Concave Mirrors Any incident ray traveling parallel to the principal axis on the way to the mirror will pass through the focal point upon reflection. Any incident ray passing through the focal point on the way to the mirror will travel parallel to the principal axis upon reflection.

36 These two rules of reflection are illustrated in the diagram below.

37 Ray Diagrams - Concave Mirrors Step-by-Step Method for Drawing Ray Diagrams 1. Pick a point on the top of the object and draw two incident rays traveling towards the mirror.

38 2. Once these incident rays strike the mirror, reflect them according to the two rules of reflection for concave mirrors. Place arrowheads upon the rays to indicate their direction of travel. Extend the rays past their point of intersection.

39 3. Mark the image of the top of the object.

40 4. Repeat the process for the bottom of the object.

41

42 Ray Diagram for the Formation of a Virtual Image Observe that in this case the light rays diverge after reflecting off the mirror. When light rays diverge after reflection, a virtual image is formed. When the object in located in front of the focal point, its image is an upright and the enlarged image is located on the other side of the mirror. ** Virtual images produced by mirrors (both plane and curved) are always upright and always located on the other side of the mirror.**

43 Optics Bench Interactive and Name that image Interactive on Physicsclassroom.com

44 Image Characteristics for Concave Mirrors

45

46 The Mirror Equation - Concave Mirrors Mirror Equation Magnification Equation

47 Mirror Equation Positive h i Upright Image (Virtual Image) Negative h i Inverted Image (Real Image) Positive d i Real Image (Image located on the object s side of the mirror) Negative d i Virtual Image (Image located behind the mirror)

48 Example Problem #1 A 4.00-cm tall light bulb is placed a distance of 45.7 cm from a concave mirror having a focal length of 15.2 cm. Determine the image distance and the image size. d i = 22.8 cm h i = cm Example Problem #2 A 4.0-cm tall light bulb is placed a distance of 8.3 cm from a concave mirror having a focal length of 15.2 cm. (NOTE: this is the same object and the same mirror, only this time the object is placed closer to the mirror.) Determine the image distance and the image size. d i = cm h i = 8.8 cm

49 Spherical Aberration Aberration - a departure from the expected or proper course. (Webster's Dictionary) Any incident ray that strikes the outer edges of the mirror is subject to this departure from the expected or proper course.

50

51 A parabolic mirror is substituted for a spherical mirror. Parabolic mirrors create sharp, clear images that lack the blurriness which is common to those images produced by spherical mirrors.

52 Reflection and Image Formation for Convex Mirrors Anatomy of a Convex Mirror *Convex mirrors produce virtual images. A convex mirror is sometimes referred to as a diverging mirror.

53 Reflection and The Formation of Images An image is the location in space where it appears that light diverges from. The point of intersection of all extended reflected rays is the image location of the object. virtual image

54 Two Rules for Convex Mirrors: Any incident ray traveling parallel to the principal axis on the way to a convex mirror will reflect in such a manner that its extension will pass through the focal point. Any incident ray traveling towards a convex mirror such that its extension passes through the focal point will reflect and travel parallel to the principal axis.

55 Step-by-Step Procedure for Drawing Ray Diagrams 1. Pick a point on the top of the object and draw two incident rays traveling towards the mirror.

56 2. Once these incident rays strike the mirror, reflect them according to the two rules of reflection for convex mirrors.

57 3. Locate and mark the image of the top of the object.

58 4. Repeat the process for the bottom of the object.

59 Image Characteristics for Convex Mirrors The diagrams above show that in each case, the image is located behind the convex mirror a virtual image an upright image reduced in size (i.e., smaller than the object)

60 Object distance vs. Image distance Object Height vs. Image Height

61 Mirror Equation The Mirror Equation - Convex Mirrors Magnification Equation

62 Example Problem #1 A 4.0-cm tall light bulb is placed a distance of 35.5 cm from a convex mirror having a focal length of cm. Determine the image distance and the image size. d i = cm h i = 1.02 cm

63 All the Slides on this PowerPoint and the previous ppt were made using the information from the website Please refer to that website for clarifications or further explanations for the diagrams. Also do the review questions for the respective chapters.