3rd year Education Student at the University of Johannesburg

1. PHYSICAL SCIENCE
GRADE 11 TOPIC

2. LIGHT: Geometrical
Optics
1. Reflection of light
2. Refraction of light
3. Lenses

3. Nature of light
 Light is a form of energy
 Light is a form of a word motion
 The way in which light radiates from its source is similar to the way in which
it ripples spread outwards across a pond.

4. ● Everyday life situations that involve refraction of light.
● How the direction of light as it passes from one medium
to another is associated with a change in velocity and
wavelength.
● Provide visual examples to help you understand how
refraction of light occurs.

5. REFRACTION OF LIGHT

6. 3rd period

7. Refraction of Light
• Refraction is the bending of a
wave as it passes at an angle
from one medium into another.
• this occurs when the light’s
velocity changes.

8. Examples
• Glass, water, ice, diamonds, and quartz
are all examples of transparent media
through which light passes through.
* Keep in mind that the speed of light in
these material is different.

9. Direction of Light
• Light travels in straight lines until it encounters another
material where it is partially reflected and partially
transmitted.
• The angle of the ray when transmitted through the
material changes and depends on the speed of light in
the two materials.

10. cont…
• As light travels through a given medium, it travels in a straight line. However,
when light passes from one medium into a second medium, the light path
bends.
• Refraction occurs only at the boundary; once the light has crossed the
boundary between the two medias, it continues to travel in a straight line.
Now the direction of that line is different than it was in the former medium.

11. For Example:

12. Example (cont.):

13. Think about it
Refraction of light happens everywhere.
Take a moment and ask yourself:
“Why do fish look larger in the water?”
“What causes a spoon to appear bent in a glass of water?”
“Why does light travel indefinitely in an optical cable?”
And the most common question, “How are rainbows, and
mirages formed?”

15. Lenses

16. Refraction
 Waves
bend
towards
the
normal
when
entering
a more
dense
medium.
Incident ray
Refracted ray

17. Converging Lenses

18. Diverging Lenses

19. Ray Diagrams - Optical Centre
Principle axis
.
F

20. Optical Centre
Principle axis
Light rays passing along the
principle axis are not
refracted as they strike both
surfaces at 90°
Any ray
passing
through the
Optical
Centre can
be thought of
as passing
straight
through.
In a thin lens the displacement is negligible.

21. REFLECTION OF LIGHT
We can see
 luminous objects: as they give off
light which enters our eyes.
Non-luminous objects: as they reflect
light from a source to our eyes.

22. NATURE OF LIGHT
Light is a form of energy.
Light is a form of wave motion.
The way in which light radiates from its source is similar
to the way in which ripples spread outwards across a
pond.

23. NATURE OF LIGHT
Light travels at a speed of 3 x 108 m/s
through empty space.
Light can be detected by human
eye.
This speed is equivalent to travelling 7 times round
the Earth in less than a second!
Light travels in straight lines.

24. Light travels in straight lines.

25. Light travels in straight lines.

26. LIGHT RAYS
The path along which light energy travels
is called a ray.
A light ray
A bundle of light rays is a beam of light.
Line represents the path along which light travels.
Arrow represents the direction in which light travels.

27. LIGHT BEAMS
3 different types of light beams :
Parallel Beam : Light rays travels from very far away
Divergent Beam : Light rays from a point source (not far
away)
Convergent Beam : Light rays meet at a point

28. A reflecting surface
Any shiny (smooth) surface.
E.g a plane mirror
Symbol of a plane mirror
reflecting surface

29. TERMS USED IN THE
STUDY OF REFLECTION
The incident ray
The ray that approaches the mirror.
incident ray

30. The reflected ray
The ray that bounces off the mirror.
reflected rayincident ray

31. TERMS USED IN THE
STUDY OF REFLECTION
The point of incidence
The point where the incident ray meets the mirror.
reflected rayincident ray
point of incidence

32. The normal
The line that is perpendicular (at 90o) to the mirror.
normal
reflected rayincident ray

33. The angle of incidence is represented by: i
The angle between the incident ray and the normal.
normal
reflected rayincident ray
i

34. The angle of reflection is represented by r
The angle between the reflected ray and the normal.
normal
reflected rayincident ray
i r

35. The angle of incidence is equal to the
angle of reflection.
i = r
normal
reflected rayincident ray
i r

36. The incident ray, the reflected ray and
the normal at the point of incidence all
lie on the same plane.
We always see all of them on the flat piece of
surface.

39. The image is virtual.
The image is upright.
The image formed has the same size as
the object.
Image cannot be formed on the screen.
Light rays do not meet at the image position.
It is an imaginary image.

40. IMAGE IN A PLANE MIRROR
The image is as far
behind the mirror as
the object is in front of
the mirror.
Object distance d1 = Image distance d2
d1d2

41. IMAGE IN A PLANE MIRROR
The image is laterally inverted (left-to-
right inversion)
Left side of the object becomes the right side of the image.

42. The following slides shows how you
can apply laws of reflection

43. To locate image formed in a plane mirror.
EYE
O

44. Step 1 : Locate the image position.
EYE
I
O

45. Step 2 : Draw reflected rays
(connect Image I to eye)
EYE
I
O

46. Step 3 : Draw incident rays.
(connect object O to reflected rays)
EYE
I
O

47. USES OF REFLECTION
Periscope
Mirror in meter
Optical testing
Other uses

48. This is commonly
called short
sighted.
Distant object
brought ‘closer’
Distant objects
the lens is not
stretched
enough. (Too
fat)
Rays are focused in
front of retina.
Object close up are
focused clearly.
A diverging lens
would cause
distant rays to
focus on the retina
and normal sight
is restored.
Short Sighted

49. Compound Microscope
F•
2
F
F F 2
F
View this slide as slide show!

50. REFERENCES
• The Broken Pencil. (n.d.). The Broken Pencil. Retrieved March 06, 2014, from
http://www.physicsclassroom.com/mmedia/optics/bp.cfm
• Changing the Speed of Light. (n.d.). Optics For Kids. Retrieved March 06, 2014,
from http://www.optics4kids.org/home/teachersparents/articles/the-
refraction-of-light/
• The Direction of Bending. (n.d.). The Direction of Bending. Retrieved March
06, 2014, from http://www.physicsclassroom.com/class/refrn/U14L1e.cfm
• Refractrion of Light. (n.d.). http://www.physicsclassroom.com. Retrieved
March 06, 2014, from http://www.ece.gatech.edu/academics/outreach/step-
up/lesson_plans/2010/Refraction/REFRACTION-OF-LIGHT.pdf

51. • refraction of light. (n.d.). refraction of light. Retrieved March 06, 2014,
from
https://www.google.com/search?q=refraction+of+light&source=lnms&tbm
=isch&sa=X&ei=TnluUpm9FNHpkAfSroC4AQ&sqi=2&ved=0CAcQ_AUoA
Q&biw=1366&bih=664#imgdii=_
• Refraction and Sight. (n.d.). Refraction and Sight. Retrieved March 06,
2014, from http://www.physicsclassroom.com/class/refrn/u14l1b.cfm
• http://www.slideshare.net/AlexanderZhongPing/physics-light-
21211682?qid=a46f0666-227d-45cb-a5f9-
70add51ddede&v=qf1&b=&from_search=6

52. H T T P : / / W W W . S L I D E S H A R E . N E T / M I N E N H L E Z / M S - Z U N G U -
2 0 1 2 2 1 2 0 0 - 3 1 9 8 3 9 8 5
Link to my presentation