1. J.M. Gabrielse Ray Diagrams

2. J.M. Gabrielse Quiz 1.Describe the difference between specular and diffuse reflection. 2.Define transparent. Give an example of a transparent object. 3.Define translucent. Give an example of a translucent object. 4.Define opaque. Give an example of a opaque object.

3. J.M. Gabrielse A ray of light is an extremely narrow beam of light.

4. J.M. Gabrielse All visible objects emit or reflect light rays in all directions.

5. J.M. Gabrielse Our eyes detect light rays.

6. J.M. Gabrielse We see images when light rays converge in our eyes. converge: come together

7. J.M. Gabrielse How Light Travels Rectilinear Propagation: Light travels in a straight line. When light strikes an opaque object, directly behind the object a shadow is created.

8. J.M. Gabrielse The part of a shadow where no light hits (directly behind the object) is called the umbra. Part of a shadow that receives some light is called the penumbra.

9. J.M. Gabrielse Mirrors object image It is possible to see images in mirrors. This is a plane mirror, such as you would see in a bathroom.

10. J.M. Gabrielse Mirrors reflect light rays.

11. J.M. Gabrielse Interactive mirror activity Students can manipulate mirrors to reflect light in different directions: http://www.bbc.co.uk/schools/ks2bitesize/sci ence/activities/see_things.shtml Now try this one: http://www.bbc.co.uk/schools/scienceclips/a ges/10_11/see_things_fs.shtml

12. J.M. Gabrielse Reflection (bouncing light) Reflection is when light changes direction by bouncing off a surface. When light is reflected off a mirror, it hits the mirror at the same angle (the incidence angle, i) as it reflects off the mirror (the reflection angle, r). The normal is an imaginary line which lies at right angles to the mirror where the ray hits it. ri Mirror normal incident ray reflected ray

13. J.M. Gabrielse The Ray Model of Light

14. J.M. Gabrielse Incident Ray: Ray of light that travels towards a reflecting surface. Angle of Incidence (i): The angle between the incident ray and the normal. Normal: The line drawn from the point of incidence at 90° to the surface of the optical device.

15. J.M. Gabrielse Point of Incidence: The spot where the incident ray strikes the reflecting surface. Angle of Reflection (r) : The angle between the reflected ray and the normal. Reflected Ray: A ray of light that bounces off a reflecting surface.

16. J.M. Gabrielse Virtual Images When an object's image lies behind the mirror, the image is called a virtual image.

17. J.M. Gabrielse Plane Mirrors (flat mirrors) How do we see images in mirrors?

18. J.M. Gabrielse Plane Mirrors (flat mirrors) objectimage Light reflected off the mirror converges to form an image in the eye. How do we see images in mirrors?

19. J.M. Gabrielse Plane Mirrors (flat mirrors) objectimage Light reflected off the mirror converges to form an image in the eye. The eye perceives light rays as if they came through the mirror. Imaginary light rays extended behind mirrors are called sight lines. How do we see images in mirrors?

20. J.M. Gabrielse Plane Mirrors (flat mirrors) objectimage Light reflected off the mirror converges to form an image in the eye. The eye perceives light rays as if they came through the mirror. Imaginary light rays extended behind mirrors are called sight lines. The image is virtual since it is formed by imaginary sight lines, not real light rays. How do we see images in mirrors?

21. J.M. Gabrielse Images in a plane mirror are the same size and distance away from the mirror. For Example: A dog of 50 cm tall is 4 m in front of a plane mirror. –What is the height of its image? –If the dog moves 2 m away from the mirror, how will the size of its image be affected? Hint: Size of the image = size of the object

22. J.M. Gabrielse Figure 1r shows how the image formed by a plane mirror is constructed. Note that the image I must be: –the same size as the object, (2m tall) –as far behind the mirror as the object is in front, (3m away from the mirror) –Have the same orientation (upright).

23. J.M. Gabrielse Drawing an Image formed by a Plane Mirror Construct the image of the object.

24. J.M. Gabrielse Draw a cone of rays from I1 to the eye. Use dotted lines for rays behind the mirror since they are not the actual path.

25. J.M. Gabrielse Draw two rays from O1 to the points where the rays from I1 meet the mirror.

26. J.M. Gabrielse Repeat steps ii and iii for I2 and O2.

27. J.M. Gabrielse Characteristics of Images in Plane Mirrors S(size) Image size is equal to object size. P(position) Image distance is equal to object distance. O(orientation) The image is upright. (Its orientation is the same as that of the object.) T(type) The image is virtual (object's image lies behind the mirror). Another interesting feature is that all images in a mirror are reversed, right to left and left to right, compared to the objects being reflected.