1. Web Link: Reflection, Refraction & Diffraction
Millions of light rays reflect from objects and enter our eyes – that’s how we see them!
When we study the formation of images, we will isolate just a few useful rays: or
Web Link: Reflection, Refraction & Diffraction

2. i = r i = incident angle r = reflected angle Reflection
measured from the normal
r = reflected angle
A line  to the surface at the point of incidence
i = r
Law of reflection

3. Web Link: Plane mirror image
Plane (flat) mirrors
Web Link: Plane mirror image
To locate the image:
1) Draw 2 different rays leaving the same point.
2) Draw their reflections.
3) Extend the reflections behind the mirror.
4) The point where they meet locates the image.

4. There are two different types of images:
Real image Light rays actually meet at that point
Virtual image Light rays only appear to come from that point
Which type do you get from a plane mirror ?

5. Finding the image position

6. Curved Mirrors

8. When mirror surfaces are curved instead of flat, strange things happen……

12. Convex Mirrors

15. Dentists Mirror

16. Traffic Mirror

18. Spherical Mirrors
concave side
convex side

19. Spherical Mirrors Centre of sphere
A ray from the centre (of curvature) is on the normal
The ray bounces straight back

20. Parallel Rays and Concave Mirror
Focal point F
Centre of curvature C
Rays parallel to the axis reflect through the focal point

21. Rays from the Focal Point
Rays from the focal point reflect parallel to the axis

22. Rays from the Centre of Curvature

23. Headlight Mirror

24. Liquid Mercury Mirror

25. Telescope

26. Solar Heater

28. Why could this be dangerous??

29. Now we’ll see how to find the position of an image in a concave mirror.

30. Locating Images: Ray Tracing For a Concave Mirror:
Ray #1: Parallel to the axis Relects through F
Ray #2: Through F Reflects parallel to axis F
Ray #3:
To pole and back at
same angle F

31. Object outside C
Image is….. C F

32. Object between F and C
Image is….. C F
SCREEN

33. Object inside F
Image is….. C F
EYE

34. The Mirror Equation C F f do
The Mirror Equation
f = mirror’s focal length (+ for concave)
do = distance between object and mirror
di = distance between image and mirror
+ for in front of mirror (real)
- for behind mirror (virtual)

35. What about the size of the image ??
ho = height of object
hi = height of image
m = magnification
m>1 if the image is larger than object
m<1 if the image is smaller than object

36. The mathematical proof
By similar triangles…

37. Convex Mirrors

40. Dentists Mirror

41. Traffic Mirror

42. Parallel Rays and Convex Mirror
Focal point F
Rays parallel to the axis reflect as if they came from
the focal point

44. Convex mirrors give a wide field of view

45. Special Rays for Convex Mirrors
Ray 1 is parallel to the axis. It reflects from the direction of “F” F
Ray 2 goes to the pole and bounces off at the same angle. F

46. Images in Convex Mirrors
Image is …… F

47. Object is in front of C: Image is always real, smaller, and inverted C
Results: Ray Tracing for concave mirrors (in each case, draw in the 3 rays for practice)
Object is in front of C: Image is always real, smaller, and inverted C F
Object between C and F: Image is always real, larger, and inverted C F
Object between F and mirror: Image is always virtual, larger and upright C F
Ex: Makeup mirror

48. Wherever the object is: Image is always virtual, smaller and upright
Results: Ray Tracing for convex mirrors (draw in the 3 rays for practice)
Wherever the object is: Image is always virtual, smaller and upright C F
Ex: Car side mirrors
Convex mirrors widen the field of view
“Objects in mirror are closer than they appear”
Web Link: Ray tracing

49. The Mirror Equation works for both concave and convex mirrors:do
f = mirror’s focal length (- for convex )
do = distance between object and mirror
di = distance between image and mirror
+ for in front of mirror (real)
- for behind mirror (virtual)
The Mirror Equation

50. What about the size of the image ??
ho = height of object
hi = height of image
m = magnification
m>1 if the image is larger than object
m<1 if the image is smaller than object
Also ….

51. Ex:
80 cm
15 cm
The mirror’s focal length is 30 cm. Find the location, size and orientation of the image of the cat.

52. 15 cm
1) Sketch the ray diagram
List information. d0 = 80 cm
di = ?
f = 30 cm
3) Formula and substitution.

53. 15 cm
size =
Nature is:
Real, inverted, diminished

54. Excellence Question:
1.6 m
50 cm
The mirror’s radius of curvature is 80 cm. Find the height of Jojo’s image.

55. Excellence Question:
1.6 m
80 cm
The mirror’s radius of curvature is 60 cm. Find the location, size and orientation of Hannah’s image.