1. Light
Reflection

2. What do we see?
All objects we see with our eyes are either luminous (give off light) eg the sun.

3. Or illuminated (reflect light) eg the moon.

4. Illumination The further from the light, the less the illumination.
Illumination is inversely proportional to the distance squared.

5. How you see Your brain believes light to travel in straight lines.
An illuminated object reflects light in many directions but only those rays coming towards your eye are “seen”.

6. For all plane mirrors, the distance from the mirror to the object is equal to the distance from the mirror to the image.

7. Law of reflection
Angle of incidence = angle reflection.

8. Which is the angle of incidence and which the angle of reflection?

9. Draw the reflected rays

10. Ray Diagrams

12. Parallax – the apparent movement.
the farther an object, the smaller is its parallax, and its converse, the smaller the parallax, the farther the object

13. Optical Illusions
Link to tour

14. Curved mirrors

15. Concave (converging mirrors)
C-centre curvature
r- radius curvature
F- principal focus point
f-focal length
A=P=pole
Sun demo.

16. A curved mirror is a small part of a sphere’s surface.
Light rays parallel to principal axis are reflected to one point – the principal focus F
Also in reverse – headlights.
f=r/2

17. 2 vital rules for converging 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

18. Ray Diagrams Ray diagrams are drawn to find details of an image. Size
Nature (inverted or upright, virtual or real, enlarged or diminished)
Position

19. How to draw ray diagrams
Draw principal axis
Mirror line
Object

20. Next a ray parallel to the principal axis is reflected through F

21. Next a ray from the top is drawn thro’ F and reflected parallel to the principal axis
A ray aimed at the pole reflects at the same angle

23. Exercises
Draw a ray diagram similar to the one before but with the object located behind C.
And between C and F.

25. Draw a ray diagram with the object between F and the mirror.

26. Note that image is upright, magnified and virtual.

27. And finally, with the object at F

29. In Summary

30. Convex (Diverging) Mirrors
Convex mirrors follow similar rules.

31. Important rules for convex mirrors
Ray parallel to principal axis reflects as if it comes from the focus
Ray aimed at focus reflects parallel to principal axis
Ray aimed at P reflected straight back

32. Exercise
Draw an accurate ray diagram showing the image formed from a 3.0 cm object 7.0 cm in front of a convex mirror of focal length 5.0 cm.
How high does the image appear?
Describe the image from these words
enlarged, same size, diminished, upright, inverted, real, virtual.

33. Formulae for spherical mirrors
Descartes’ formula
di distance to image
do distance to object

34. Magnification
m=hi/ho = di/do

35. Exercise
Michael is shaving with his face 12 cm from a concave mirror of focal length 12.5 cm.
What is the magnification of the image of his face?

36. di =-300cm ( negative sign shows virtual image) m = di/do = 300/12=25
Answer
1/f = 1/di + 1/do
1/12.5 = 1/di + 1/12
di =-300cm ( negative sign shows virtual image)
m = di/do = 300/12=25

37. Exercise
A convex mirror has f 10 cm. Calculate the position and size of a 10cm object 6cm in front of mirror.

38. Answer do = 6 cm, f = -10 cm, ho = 10 cm 1/di=1/10 – 1/6 di = -3.75 cm
m = di/do = 0.625
hi = mho = x 10 = 6.25 cm

39. Activity 5b on page 67