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. Light travels in straight lines

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

5. 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.

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

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

9. 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

10. F

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

12. 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.

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

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

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

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

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

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

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

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

21. 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

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

23. 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

24. 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

25. 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.

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

27. 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.

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

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

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

32. 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

33. 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

34. 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.

35. 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.

36. H/W
LC Ord 2006 Q2

37. Refractive Index
Ratio of speeds

38. Real and Apparent Depth
A pool appears shallower

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

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

42.      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.

43. Refraction out of glass or water
Light stays in denser medium
Reflected like a mirror
Angle i = angle r

44. Snell’s Window

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

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

47. Mirages

48. Critical Angle
Varies according to refractive index

49. 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.

50. 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.

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

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

53. H/W
LC Ord 2003 Q7

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

55. Ray Diagrams
Optical Centre 2F F F

56. 2F F

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

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

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

60. Object at F
Image is at infinity F

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

62. H/W
Draw the 5 ray diagrams for the converging lens and the diagram for the diverging lens .
Write 3 characteristics of each image.

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

64. 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

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

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

67. 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.

68. H/W
LC Ord 2002 Q3

70. 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.

71. Accommodation internet

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

73. 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

74. 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

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

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

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

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

80. 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

81. 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

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