1. Introduction to Ray Diagrams How to draw them for Curved Mirrors (please view this slide show in presentation view by pressing F5)

2. Curved Mirrors In the previous section you learned about plane mirrors –Mirrors that are flat In this section you will begin to look at what happens to light when it reflects off curved surfaces

3. Concave Mirrors A mirror that has a surface that curves in like a bowl, is called a concave mirror or converging mirror. –To remember the shape of a concave mirror, think of the phrase: “You go into a cave.” The light goes into the bowl of the mirror.

4. Concave Mirrors (cont’d) We use concave mirrors for many different reasons. –Examples include, microscopes, telescopes, flashlights, cosmetic mirrors, car headlights.

5. Curved Mirror Terminology Remember all those definitions you did at the first of this unit? Now you will start to understand what some of those definitions mean

6. Curved Mirror Terminology (cont’d) Curved mirrors follow the same laws of reflection as plane mirrors –In this case you will be looking at a concave mirror. The difference is that when hitting a curved mirror with parallel rays of light, the light all reflect off the mirror to single point called the focal point focal point concave mirror

7. Curved Mirror Terminology (cont’d) The middle part of the curved surface of a mirror is called a vertex The imaginary line drawn through the vertex at a right angle to the surface of the mirror is called the principal axis or normal focal point mirror vertex principal axis

8. Curved Mirror Terminology (cont’d) The distance from the vertex to the focal point in called the focal length. mirror vertex principal axis focal point focal length

9. Curved Mirror Terminology (cont’d) The distance between the vertex and the object being imaged in the mirror is represented by d o The distance between the vertex and the image created by the mirror is referred as d i Notice how the image is inverted mirror vertex principal axis object image focal point dodo didi

10. Curved Mirror Terminology (cont’d) A real image is an image formed by light rays that come from the location of the image –Meaning if a piece of paper was put at the spot where the real image forms, a focussed image would appear on the paper.

11. Ray Diagrams for Concave Mirrors Ray diagrams allow a person to determine if an image will be formed by an object whose light is reflecting off a mirror The diagram also determines whether the image formed is real or virtual Finally if an image is formed, the ray diagram will show you where the image will be located

12. Ray Diagrams for Concave Mirrors (cont’d) Usually to practice drawing a ray diagram an arrow is used as the object You will need to draw two rays to find out where the image is located. –The place where the reflected rays intersect is the position of the image –If there is no place where the reflected rays overlap, then there is no real image formed –However if the back reflecting rays insect behind the mirror a virtual image is formed The following slides will illustrate how each case occurs

13. Ray Diagrams for Concave Mirrors (cont’d) The image formed by a concave mirror depends on how far away the object is from the focal point If the object is far away from the focal point, then the image formed is inverted mirror vertex principal axis focal point object inverted image

14. focal point mirror vertex principal axis Ray Diagrams for Concave Mirrors (cont’d) 1. The first ray travels horizontally, parallel to the principal axis 2. This ray reflects off the mirror’s surface and travels through the focal point 3. The second ray travels through the focal point 4. This ray reflects off the mirror’s surface and travels horizontally, parallel to the principal axis 5. A third ray can be drawn to confirm the location of the image as shown. The incident ray is drawn from the object to the vertex. The reflected ray comes off the mirror at the same angle as the incident ray.

15. Ray Diagrams for Concave Mirrors (cont’d) The point where the two reflected rays cross is where the image forms Notice how this image is larger and inverted. Since this image is on the same side of the mirror as the object, a real image is formed This occurs when the object is at a greater distance from the mirror than the focal point focal point mirror vertex principal axis

16. Ray Diagrams for Concave Mirrors (cont’d) focal point mirror vertex principal axis virtual image When the object is at a distance that is closer to the mirror than the focal point, something different happens to the rays. These rays will never intersect Only two rays can be drawn in this case The only way to locate the image that is formed is by looking at the continuation of the reflected lines behind the mirror. They are drawn using dotted lines Where the two dotted lines intersect is the location of the image. Since the image is behind the mirror, it is called a virtual image. It is upright and larger than the original image.

17. Ray Diagrams for Concave Mirrors (cont’d) focal point mirror vertex principal axis These rays will never intersect When the object is at the focal point, no image is formed.

18. Ray Diagrams for Concave Mirrors (cont’d) The closer the object gets to the focal point, the larger the image becomes. Go to www.explorelearning.com and login www.explorelearning.com Go to the “Ray Tracing (Mirrors)” Gizmo to see how moving the object closer to the focal point makes it bigger. –Choose concave mirror in the mirror options –You’ll have to move the focal point to the closest possible position to observe the difference effectively

19. Magnification You may have already noticed how the object and it’s reflected image are, in many cases, not the same size. When describing how much bigger or smaller the image is than the original object we use the term magnifaction. The comparison between the object and it’s image can be described in three ways 1. same size 2. enlarged (larger than the object) 3. Diminished (smaller than the object)

20. Magnification (cont’d) Magnification can be calculated using the following formula It can also be calculated using distance from the image to the mirror and from the object to the mirror

21. Convex Mirrors A mirror with a surface curved outward is called a convex mirror or diverging mirror. Instead of focussing light rays to a single focal point, the convex mirror spreads them out –One can think of the rays being spread out from a single point –This point is the focal point for the backside of the mirror

22. Convex Mirrors We use convex mirrors everyday. –They can used for store security, side view mirrors in cars, for safety at intersections

23. Convex Mirrors (cont’d) Convex mirrors do not form a real image, only a virtual image. focal point mirror principal axis These rays will never intersect. Therefore, no real image will be formed. virtual image

24. Ray Diagrams for a Convex Mirrors focal point mirror principal axis 1. Draw the first ray parallel to the principal axis from the object to the mirror’s surface. virtual image 2. Draw another line away from the mirror’s surface in line with the focal point. 3. Draw a dotted line from the surface of the mirror where the first line hits the mirror’s surface to the focal point. 4. Draw a second ray directly from the object to the mirror’s surface in line with the focal point. 6. Draw a dotted line from the surface of the mirror where the second ray hits the mirror’s surface parallel with the principal axis. 5. Another line is drawn away from the mirror’s surface parallel to the principal axis. The point where the two dotted lines intersect is where the virtual

25. Ray Diagrams for Convex Mirrors (cont’d) Go to www.explorelearning.com and login www.explorelearning.com Go to the “Ray Tracing (Mirrors)” Gizmo to see how moving the object closer to and further away from the mirror makes affects the image formed. –Choose convex mirror in the mirror options

26. Draw Ray Diagrams Go to the word document for this lesson and print out the ray diagram pages. Complete the ray diagrams for the concave and convex mirrors. –You only need to do rays for the tip of the arrow, just like you learned in the previous slides.

27. Questions from the Textbook Go to page 433 in the book and answer questions 4, 6, 8, 11 and 12 in the document for this lesson