1. Light
By Neil Bronks

2. Light is a form of energy
Crooke’s Radiometer proves light has energy
Turns in sunlight as the light heats the black side

3. Primary and secondary colours
A secondary colour is 2 primary colours mixed
Complimentary are that combine to make white

4. Light travels in straight lines

5. Reflection-Light bouncing off object
Angle of incidence = Angle of reflection
Normal
Incident ray
Reflected ray
Angle of incidence
Angle of reflection
Mirror

6. Laws of Reflection
The angle of incidence ,i, is always equal to the angle of reflection, r.
The incident ray, reflected ray and the normal all lie on the same plane.

7. Virtual Image An image that is formed by the eye
Can not appear on a screen d d

9. Real Image
Rays really meet
Can be formed on a screen F 2F

10. Concave Mirror Object Pole F Principal Axis
All ray diagrams in curved mirrors and lens are drawn using the same set of rays.
Concave Mirror
Object
Pole F
Principal Axis

11. F

12. F You can draw any ray diagram by combining 2 of these rays
The only difference is where the object is based. F

13. Your turn Paper and pen (Ruler naturally)2F F

14. Ray Diagrams- Object outside 2F
1/. Inverted
2/. Smaller
3/. Real 2F F
The images can be formed on a screen so they are real.

15. Object at 2F 1/. Inverted 2/. Same Size 3/. Real F 2F
The image is at 2F

16. Object between 2F and F 1/. Inverted 2/. Magnified 3/. Real 2F F
The image is outside 2F

17. Object at F F 2F
The image is at infinity

18. Object inside F 1/. Upright 2/. Magnified 3/. Virtual F
The image is behind the mirror

19. Convex Mirror 1/. Upright 2/. Smaller 3/. Virtual
The image is behind the mirror
1/. Upright
2/. Smaller
3/. Virtual F

20. Convex Mirror – only one ray diagramF
The image is behind the mirror

21. Uses of curved mirrors Concave Mirrors Convex Mirror Security Mirrors
Dentists Mirrors
Make –up mirrors
Convex Mirror
Security Mirrors
Rear view mirrors

22. u v Calculations Use the formula f=focal length u=object distance
v=image distance
Use the formula u F v

23. Example
An object is placed 20cm from a concave mirror of focal length 10cm find the position of the image formed. What is the nature of the image?
Collect info f=10 and u=20
Using the formula 10 20
V=20cm real

24. Magnification What is the magnification in the last question?
Well u=20 and v=20 As 20
m=1
Image is same size 2

25. Example
An object is placed 20cm from a concave mirror of focal length 30cm find the position of the image formed. What is the nature of the image?
Collect info f=30 and u=20
Using the formula
V=60cm Virtual

26. Example
An object is placed 30cm from a convex mirror of focal length 20cm find the position of the image formed. What is the nature of the image?
Collect info f=-20 and u=30
The minus is
Because the
Mirror is
convex
Using the formula
V=60/5cm =12cm Virtual

27. Questions
An object 2cm high is placed 40cm in front of a concave mirror of focal length 10cm find the image position and height.
An image in a concave mirror focal length 25cm is 10cm high if the object is 2cm high find the distance the object is from the mirror.

28. MEASUREMENT OF THE FOCAL LENGTH OF A CONCAVE MIRROR
Crosswire u
Lamp-box
Screen v

29. Approximate focal length by focusing image of window onto sheet of paper.
Place the lamp-box well outside the approximate focal length
Move the screen until a clear inverted image of the crosswire is obtained.
Measure the distance u from the crosswire to the mirror, using the metre stick.
Measure the distance v from the screen to the mirror.
Repeat this procedure for different values of u.
Calculate f each time and then find an average value.  
Precautions The largest errors are in measuring with the meter rule and finding the exact position of the sharpest image.

30. H/W
2007 H q3

31. Refraction The fisherman sees the fish and tries to spear it
Fisherman use a trident as light is bent at the surface

33. Refraction into glass or water
Light bends towards the normal due to entering a more dense medium
AIR
WATER

34. Refraction out of glass or water
Light bends away from the normal due to entering a less dense medium

35. Refraction through a glass block
Light bends towards the normal due to entering a more dense medium
Light slows down but is not bent, due to entering along the normal
Light bends away from the normal due to entering a less dense medium

36. Refraction through a glass block
Angle of Incidence=i
Angle of Refraction=r

37. Laws of REFRACTION
The incident ray, refracted ray and normal all lie on the same plane
SNELLS LAW the ratio of the sine of the angle of incidence to the sine of the angle of refraction is constant for 2 given media.
sin i = n (Refractive Index)
sin r

38. Proving Snell’s Law Sin i i r Sin r
A straight line though the origin proves Snell’s law.
The slope is the refractive index.

39. Proving Snell’s Law Sin i i r Sin r
Laser
Sin i i
Protractor
Glass Block r
Sin r
A straight line though the origin proves Snell’s law.
The slope is the refractive index.

40. H/W
LC H 2010 Q3

41. Refractive Index
Ratio of speeds

42. Real and Apparent Depth
A pool appears shallower

44. REFRACTIVE INDEX OF A LIQUID
MEASUREMENT OF THE
REFRACTIVE INDEX OF A LIQUID
Cork
Pin
Apparent depth
Mirror
Real depth
Water
Image
Pin

45. Finding No Parallax – Looking Down
Pin at
bottom
Pin
reflection
in mirror
No Parallax
Parallax

46.      Set up the apparatus as shown.
    Adjust the height of the pin in the cork above the mirror until there is no parallax between its image in the mirror and the image of the pin in the water.
    Measure the distance from the pin in the cork to the back of the mirror – this is the apparent depth.
    Measure the depth of the container – this is the real depth.
    Calculate the refractive index n= Real/Apparent
Repeat using different size containers and get an average value for n.

47. Refraction out of glass or water (From dense to less dense)
Light stays in denser medium
Reflected like a mirror
Angle i = angle r

48. Snell’s Window
(From dense to less dense

49. Finding the Critical Angle…(From dense to less dense)
2) Ray still gets refracted
1) Ray gets refracted
4) Total Internal Reflection
3) Ray still gets refracted (just!)
THE CRITICAL ANGLE

50. Semi-Circular Block Expt and on the internet click here

51. Mirages

52. Rainbow
Rain Droplets
Strong sunlight
Observer back to sun

53. Critical Angle
Varies according to refractive index

54. 2012 Question 12 (b) [Higher Level]
The diagram shows a ray of light as it leaves a rectangular block of glass. As the ray of light leaves the block of glass, it makes an angle θ with the inside surface of the glass block and an angle of 30o when it is in the air, as shown.
If the refractive index of the glass is 1.5, calculate the value of θ.
What would be the value of the angle θ so that the ray of light emerges parallel to the side of the glass block?
Calculate the speed of light as it passes through the glass.

55. Prism Question – Class Challenge
Draw the path of the light and give its angles
70o
n=1.5

56. Uses of Total Internal Reflection
Optical fibres:
An optical fibre is a long, thin, transparent rod made of glass or plastic. Light is internally reflected from one end to the other, making it possible to send large chunks of information
Optical fibres can be used for communications by sending e-m signals through the cable. The main advantage of this is a reduced signal loss. Also no magnetic interference.

57. Practical Fibre Optics
It is important to coat the strand in a material of low n.
This increases Total Internal Reflection
The light can not leak into the next strand.

58. Endoscopes (a medical device used to see inside the body):
2) Binoculars and periscopes (using “reflecting prisms”)

59. Now is a good time to get out the light demo kit

60. 2004 Question 12 (b) [Higher Level]
Give two reasons why the telecommunications industry uses optical fibres instead of copper conductors to transmit signals.
Explain how a signal is transmitted along an optical fibre.
An optical fibre has an outer less dense layer of glass. What is the role of this layer of glass?
An optical fibre is manufactured using glass of refractive index of 1.5.
Calculate the speed of light travelling through the optical fibre.

61. H/W
LC Ord 2003 Q7

62. Lenses Converging Lens Diverging Lens Two types of lenses
Focal Point
Focal Length=f
Focal Length=f
Converging Lens Diverging Lens

63. Two refractions

64. Ray Diagrams
Optical Centre 2F F F

65. 2F F

66. Drawing again! 2F F

67. Challenge
Draw the 5 ray diagrams for the converging lens and the diagram for the diverging lens .
Write 3 characteristics of each image. 2F F

68. Converging Lens- Object outside 2F
Image is
1/. Real
2/. Inverted
3/. Smaller 2F F

69. Object at 2F
Image is
1/. Real
2/. Inverted
3/. Same size 2F F

70. Object between 2F and F Image is 1/. Real 2/. Inverted 3/. Magnified

71. Object at F
Image is at infinity F

72. Object inside F
Image is
1/. Virtual
2/. Erect
3/. Magnified F

73. u v Calculations Use the formula f=focal length u=object distance
v=image distance
Use the formula u 2F F v

74. Example
An object is placed 30cm from a converging lens of focal length 40cm find the position of the image formed. What is the nature of the image?
Collect info f=40 and u=30
Using the formula v 30 40 - =
-120 40 30
V=120cm virtual

75. Magnification What is the magnification in the last question?
Well u=30 and v=120 As
120 30 4 1
Image is larger

76. MEASUREMENT OF THE FOCAL LENGTH
OF A CONVERGING LENS
Show on OPTICAL BENCH
Lamp-box with crosswire
Screen
Lens v u

77. 1.      Place the lamp-box well outside the approximate focal length
2.    Move the screen until a clear inverted image of the crosswire is obtained.
3.    Measure the distance u from the crosswire to the lens, using the metre stick.
4. Measure the distance v from the screen to the lens.
5. Calculate the focal length of the lens using
6. Repeat this procedure for different values of u.
7. Calculate f each time and then find the average value.

78. H/W
LC H 2009 Q2

80. Accommodation
The width of the lens is controlled by the ciliary muscles.
For distant objects the lens is stretched.
For close up objects the muscles relax.

81. Accommodation internet

82. Diverging Lens
Image is
1/. Virtual
2/. Upright
3/. Smaller F F

83. Example
An object is placed 30cm from a diverging lens of focal length 20cm find the position of the image formed. What is the nature of the image?
Collect info f=-20 and u=30
The minus is
Because the
Diverging lens
Using the formula
V=60/5cm =12cm Virtual

84. Example
An object is placed 30cm from a diverging lens of focal length 60cm find the position of the image formed. What is the nature of the image? (Remember f must be negative)
Collect info f=-60 and u=30
Using the formula v 30
-60 - =
-20
-60 30
V=20cm virtual

85. Magnification What is the magnification in the last question?
Well u=30 and v=20 As 20 30 2 3
Image is smaller

86. Sign Convention f Positive V either f negative V f negative V f

87. Myopia (Short Sighted)
Image is formed in front of the retina.
Correct with diverging lens.

88. Hyperopia (Long-Sighted)
Image is formed behind the retina.
Correct with a converging lens

90. Underwater Vision
Solution is a pair of goggles!
Water

91. Power of Lens Opticians use power to describe lenses. P=
So a focal length of 10cm= 0.1m is written as P=10m-1
A diverging lens with a negative focal length f=-40cm=-0.4m
Has a power of P = -2.5m-1

92. The power of the total lens is
Lens in Contact
Most camera lens are made up of two lens joined to prevent dispersion of the light.
The power of the total lens is
Ptotal=P1+ P2
P = 1/12 -1/10= cm-1
F=1/p=1/ =-60cm
F=12cm
F= -10cm

93. Glasses – Class Challenge
A certain teacher has eyes of power 64m-1 but standard eyes are 60m-1 What is the power of the lens he needs and the focal length and type of the lens?
The power is the difference 60-64=-4
The focal length is ¼ = -0.25m
The minus means a diverging lens.

94. 2006 Question 7 [Higher Level]
What is meant by the refraction of light?
A converging lens is used as a magnifying glass. Draw a ray diagram to show how an erect image is formed by a magnifying glass.
A diverging lens cannot be used as a magnifying glass. Explain why.
The converging lens has a focal length of 8 cm. Determine the two positions that an object can be placed to produce an image that is four times the size of the object?
The power of an eye when looking at a distant object should be 60 m–1. A person with defective vision has a minimum power of 64 m–1. Calculate the focal length of the lens required to correct this defect.
What type of lens is used?
Name the defect.

95. H/W
LC Higher 2002 Q12 (b)
LC Higher 2003 Q3