1. Reflection pg. 75

2. Objectives State and apply the law of reflection. Locate an image created by reflection in a plane (flat) mirror by constructing a ray diagram. Describe the image created by a plane mirror. Locate an image created by reflection in a plane mirror using several investigation techniques. Physics terms incident ray reflected ray normal incident angle reflected angle law of reflection reflection mirror ray diagram image

3. Reflection

4. Light travels in straight lines. Mirrors are optical devices that divert light using reflection. There are different kinds of mirrors based on their shape: flat mirror (AKA plane mirror) convex mirror (bulges out at the middle) concave mirror (bows inward at the middle) Reflection from mirrors

5. Light can be represented in diagrams as waves or as rays. To show the effect of mirrors and lenses, you typically use the light ray representation (AKA ray diagram). Ray representation of light

6. A ray diagram shows the paths that light rays follow in order for a person to view a point on the image of an object. Ray diagrams help explain shadow formation, and show how mirrors and lenses create images. Ray diagrams

7. Incident and reflected rays Light rays can reflect off any surface or any boundary between two materials— such as a classroom wall, or a flat mirror. Incident ray: the incoming light ray that strikes this mirror Reflected ray: the light ray that reflects off the surface of the mirror

8. Symmetry of reflection There is a symmetry in reflection: Rays close to the mirror reflect close to the mirror. Rays high above the mirror reflect high from the mirror

9. Normal: an imaginary line drawn perpendicular to the reflecting surface where the light ray strikes it. Angle of incidence: the angle between the incident ray and the normal, θ i. Angle of reflection: the angle between the reflected ray and the normal θ r. What is true about θ i and θ r ? Angles of incidence and reflection

10. The angle of incidence always equals the angle of reflection. Law of reflection Remember: measure angles with respect to the normal!

11. 1. If a light ray strikes a mirror at an angle of 35°to the normal, then what is the angle of reflection? 2. If a light ray strikes a mirror at an angle of 70°from its surface, then what is the angle of reflection? Engaging with the concepts 35° 90°- 70°= 20°

12. It is formed by an optical device through reflection or refraction. It is an organization of light rays that has the same spatial pattern as the original light rays coming from the actual object. Lens Object Image An image is an illusion created with light. What is an image?

13. ALL light rays from 1 point on the object that pass through the optical device will converge at that same point on the image. Lens Object Image What is an image?

14. 1.Images are virtual & upright Image orientation will not be flipped 2.Left-Right image reversal 3. Object distance = image distance 4. Image size = object size Ratio of image dimensions to object dimensions Plane mirrors  magnification of 1 4 Characteristics of plane mirror images

15. The object distance d o is the distance from the object to the mirror surface. The image distance d i is the distance from the image to the mirror surface. What do you notice about these two distances? dodo didi Image formation for a flat mirror

16. Image formation for a flat mirror  Method 1

17. 2. Pick 1 extreme point on image & draw reflected ray that will travel to the eye. 3.Draw incident ray for light traveling from corresponding extreme on object in mirror. 4. Repeat 2 & 3 for all other extremities of object Image formation for a flat mirror  Method 1 continued

21. 1.Draw 2 light rays incident upon the mirror 2.Draw the normal to the mirrors surface at the location each ray strikes it 3.Draw reflected rays using law of reflection 4.Extend the reflected rays until they intersect behind the mirror at the location of the image 5.Repeat to find image location for bottom of the object Image location for a flat mirror  Method 2

23. Image location for a flat mirror

25. These virtual rays are drawn with dashed lines.

26. Image location for a flat mirror

27. The distance from object to mirror equals the distance from image to mirror. d o d i Image location for a flat mirror

28. A red arrow is oriented as shown in front of a plane mirror. Sketch the image of the arrow with the correct size location, and orientation. Test your knowledge

29. The image arrow is shown in pale red. Solid black lines show the path of the light rays. Dashed lines show the path of virtual rays. Test your knowledge Each reflected ray obeys the law of reflection.

30. Homework 1.Correctly label this figure with: the normal; incident ray; reflected ray; angle of incidence; and angle of reflection. 2.What is the angle of reflection in this figure?

31. The angle of incidence and the 50° angle must add up to 90°. 1.Correctly label this figure with: the normal; incident ray; reflected ray; angle of incidence; and angle of reflection. 2.What is the angle of reflection in this figure? 40° Homework 40°

32. 3.Locate the image of this star in the flat mirror by constructing a ray diagram. Homework

33. You can use any two rays to locate the image. These are shown as examples. 3.Locate the image of this star in the flat mirror by constructing a ray diagram. Homework

34. Her face appears to be about one meter in front of the mirror. Her reflected image should therefore be located approximately one meter behind the mirror. 4.In this painting, where should the reflected image of the woman’s face be located? Homework