1. PHYSICS – Total Internal Reflection and Lenses

2. LEARNING OBJECTIVES Core
•Describe the formation of an optical image by a plane mirror, and give its characteristics
• Recall and use the law angle of incidence = angle of reflection
Describe an experimental demonstration of the refraction of light
• Use the terminology for the angle of incidence i and angle of refraction r and describe the passage of light through parallel-sided transparent material
• Give the meaning of critical angle
• Describe internal and total internal reflection
Describe the action of a thin converging lens on a beam of light
• Use the terms principal focus and focal length
• Draw ray diagrams for the formation of a real image by a single lens
• Describe the nature of an image using the terms enlarged/same size/diminished and upright/inverted
Supplement
Describe the formation of an optical image by a plane mirror, and give its characteristics
Recall and use the definition of refractive index n in terms of speed
• Recall and use the equation sin I / sin r=n
• Recall and use n = 1 / sin c
• Describe and explain the action of optical fibres particularly in medicine and communications technology
Draw and use ray diagrams for the formation of a virtual image by a single lens • Use and describe the use of a single lens as a magnifying glass • Show understanding of the terms real image and virtual image

3. Refraction of light by a semi-circular block.
Refracted Ray
Angle of Refraction R
Angle of Incidence I
Incident Ray

4. Refraction of light by a semi-circular block.
Refracted Ray
When a ray of light travels through a semi-circular block, the ray will be refracted ………
Angle of Refraction R
Angle of Incidence I
Incident Ray

5. Refraction of light by a semi-circular block.
Refracted Ray
When a ray of light travels through a semi-circular block, the ray will be refracted ………
Angle of Refraction R
Reflected Ray
Angle of Incidence I
…… but there will also be some reflection.
Incident Ray

6. There is now more internal reflection
Refraction of light by a semi-circular block.
As the incident ray approaches the ‘critical angle’ (approximately 42o) the refracted ray travels at right-angles to the normal.
Refracted Ray
Incident Ray
Reflected Ray
There is now more internal reflection

7. Refraction of light by a semi-circular block.
If the incident ray now enters the block at an angle greater than the critical angle (42o) no light is refracted.
Incident Ray
Reflected Ray

8. Refraction of light by a semi-circular block.
If the incident ray now enters the block at an angle greater than the critical angle (42o) no light is refracted.
Incident Ray
Reflected Ray
All light is now reflected at the boundary. This is known as TOTAL INTERNAL REFLECTION

9. Refraction of light by a semi-circular block.
Medium
Critical angle
Water
49o
Perspex
42o
Glass
41o
Diamond
24o
If the incident ray now enters the block at an angle greater than the critical angle (42o) no light is refracted.
Incident Ray
Reflected Ray
All light is now reflected at the boundary. This is known as TOTAL INTERNAL REFLECTION

22. Refraction Calculations

23. Refraction Calculations
Supplement
Refraction Calculations
Snell’s Law
When light is refracted, an increase in the angle of incidence i produces an increase in the angle of refraction r.

24. Refraction Calculations
Supplement
Refraction Calculations
Snell’s Law
When light is refracted, an increase in the angle of incidence i produces an increase in the angle of refraction r.
Sin i = constant
Sin r

25. Refraction Calculations
Supplement
Refraction Calculations
Snell’s Law
Air
i = 15o
r = 10o
Glass
sin 15o = 0.26
sin 10o = 0.17
= 1.5

26. Refraction Calculations
Supplement
Refraction Calculations
Snell’s Law
Air
i = 15o
i = 45o
r = 10o
Glass
r = 28o
sin 15o = 0.26
sin 10o = 0.17
= 1.5
sin 45o = 0.71
sin 28o = 0.47
= 1.5

27. Refraction Calculations
Supplement
Refraction Calculations
Snell’s Law
Air
i = 15o
i = 45o
i = 60o
r = 10o
Glass
r = 28o
r = 35o
sin 15o = 0.26
sin 10o = 0.17
= 1.5
sin 45o = 0.71
sin 28o = 0.47
= 1.5
sin 60o = 0.87
sin 35o = 0.57
= 1.5

28. Refraction Calculations
Supplement
Refraction Calculations
…and Refractive Index
Snell’s Law

29. Refraction Calculations
Supplement
Refraction Calculations
…and Refractive Index
Snell’s Law
Refractive Index = Sin i
Sin r

30. Refraction Calculations
Supplement
Refraction Calculations
…and Refractive Index
Snell’s Law
Refractive Index = Sin i
Sin r
Air
i = 45o ?
RI = 1.33
Water

31. Refraction Calculations
Supplement
Refraction Calculations
…and Refractive Index
Snell’s Law
Refractive Index = Sin i
Sin r
RI = sin i
sin r
1.33 = sin 45o
sin r = sin 45o
1.33
sin r = 0.532
r = 32o
Air
i = 45o ?
RI = 1.33
Water

32. Refraction Calculations
Supplement
Refraction Calculations
…and Refractive Index
…and Critical Angles!
Snell’s Law

33. Refraction Calculations
Supplement
Refraction Calculations
…and Refractive Index
…and Critical Angles!
Snell’s Law
If the angle of incidence is greater than the critical angle, we will get total internal reflection.

34. Refraction Calculations
Supplement
Refraction Calculations
…and Refractive Index
…and Critical Angles!
Snell’s Law
If the ray direction is reversed, the angle of incidence is now 90o, and the angle ‘c’ is now the angle of refraction (critical angle).
Critical angle
Incident Ray c
Refracted Ray

35. Refraction Calculations
Supplement
Refraction Calculations
…and Refractive Index
…and Critical Angles!
Snell’s Law
If the ray direction is reversed, the angle of incidence is now 90o, and the angle ‘c’ is now the angle of refraction (critical angle).
Critical angle
Incident Ray c
Refracted Ray
RI = sin i = sin90o
sin c sin c

36. Refraction Calculations
Supplement
Refraction Calculations
…and Refractive Index
…and Critical Angles!
Snell’s Law
If the ray direction is reversed, the angle of incidence is now 90o, and the angle ‘c’ is now the angle of refraction (critical angle).
Critical angle
Incident Ray c
Refracted Ray
RI = sin i = sin90o
sin c sin c
RI = sin c = 1
sin c RI

37. Refraction Calculations
Supplement
Refraction Calculations
…and Refractive Index
…and Critical Angles!
Snell’s Law
If the RI of glass = 1.5: sin c = 1 = c = 42o
1.5
If the ray direction is reversed, the angle of incidence is now 90o, and the angle ‘c’ is now the angle of refraction (critical angle).
Critical angle
Incident Ray c
Refracted Ray
RI = sin i = sin90o
sin c sin c
RI = sin c = 1
sin c RI

38. Snell’s Law Refraction Calculations
Supplement
Refraction Calculations
…and Refractive Index
…and Critical Angles!
Snell’s Law
The refractive index of a medium is usually denoted as ‘n’.
For a medium of refractive index n: sin c = 1 n
If the RI of glass = 1.5: sin c = 1 = c = 42o
1.5
Critical angle
Incident Ray c

39. Snell’s Law Refraction Calculations
Supplement
Refraction Calculations
…and Refractive Index
…and Critical Angles!
Snell’s Law
The refractive index of a medium is usually denoted as ‘n’.
For a medium of refractive index n: sin c = 1 n
If the RI of glass = 1.5: sin c = 1 = c = 42o
1.5
Critical angle
Incident Ray c
eg. What is the critical angle for diamond if the refractive index (n) = 2.42?
sin c = = = critical angle for diamond = 24.4o n

40. LEARNING OBJECTIVES Core
•Describe the formation of an optical image by a plane mirror, and give its characteristics
• Recall and use the law angle of incidence = angle of reflection
Describe an experimental demonstration of the refraction of light
• Use the terminology for the angle of incidence i and angle of refraction r and describe the passage of light through parallel-sided transparent material
• Give the meaning of critical angle
• Describe internal and total internal reflection
Describe the action of a thin converging lens on a beam of light
• Use the terms principal focus and focal length
• Draw ray diagrams for the formation of a real image by a single lens
• Describe the nature of an image using the terms enlarged/same size/diminished and upright/inverted
Supplement
Describe the formation of an optical image by a plane mirror, and give its characteristics
Recall and use the definition of refractive index n in terms of speed
• Recall and use the equation sin I / sin r=n
• Recall and use n = 1 / sin c
• Describe and explain the action of optical fibres particularly in medicine and communications technology
Draw and use ray diagrams for the formation of a virtual image by a single lens • Use and describe the use of a single lens as a magnifying glass • Show understanding of the terms real image and virtual image

41. Lenses and Refraction
Convex lens
Concave lens

42. Lenses and Refraction Convex lens Concave lens Converging lens
Diverging lens

43. Lenses and Refraction Convex lens Concave lens Converging lens
Diverging lens
Principal focus
Focal length

44. Lenses and Refraction Convex lens Concave lens Converging lens
Diverging lens
Principal focus
Principal focus
Focal length
Focal length

45. What happens to light as it passes through the lens?
Lenses and Refraction
What happens to light as it passes through the lens?
Convex lens

46. What happens to light as it passes through the lens?
Lenses and Refraction
What happens to light as it passes through the lens?
Convex lens

47. What happens to light as it passes through the lens?
Lenses and Refraction
What happens to light as it passes through the lens?
Convex lens

48. What happens to light as it passes through the lens?
Lenses and Refraction
What happens to light as it passes through the lens?
Convex lens
As light passes through the first face of the lens it bends towards the normal (refraction)

49. What happens to light as it passes through the lens?
Lenses and Refraction
What happens to light as it passes through the lens?
Convex lens
As light passes through the first face of the lens it bends towards the normal (refraction)
As light passes through the second face of the lens it bends away from the normal (refraction)

50. What happens to light as it passes through the lens?
Lenses and Refraction
What happens to light as it passes through the lens?
Convex lens
As light passes through the first face of the lens it bends towards the normal (refraction)
As light passes through the second face of the lens it bends away from the normal (refraction)

51. Lenses and Images
Rays from a distant object brought to focus on a screen by a convex lens.
Object
Convex lens
Image

52. The image on the screen is real and inverted (upside-down)
Lenses and Images
Rays from a distant object brought to focus on a screen by a convex lens.
Object
Convex lens
Image
The image on the screen is real and inverted (upside-down)

53. The image on the screen is real and inverted (upside-down)
Lenses and Images
Rays from a distant object brought to focus on a screen by a convex lens.
Object
Convex lens
Image
Light rays from a distant object are considered to be parallel to each other, so the image passes through the principal focus.
The image on the screen is real and inverted (upside-down)

54. Lenses and Ray Diagrams
- Predicting where a convex lens will form an image. F1 F

55. Lenses and Ray Diagrams
- Predicting where a convex lens will form an image.
Standard Ray 1 – passes through the centre of the lens
object F1 F

56. Lenses and Ray Diagrams
- Predicting where a convex lens will form an image.
Standard Ray 1 – passes through the centre of the lens
Standard Ray 2 – parallel to the principal axis, and then passes through F after leaving the lens.
object F1 F

57. Lenses and Ray Diagrams
- Predicting where a convex lens will form an image.
Standard Ray 1 – passes through the centre of the lens
Standard Ray 2 – parallel to the principal axis, and then passes through F after leaving the lens.
object F1 F
Standard Ray 3 – passes through F1, and then leaves the lens parallel to the principal axis.

58. Lenses and Ray Diagrams
- Predicting where a convex lens will form an image.
Standard Ray 1 – passes through the centre of the lens
Standard Ray 2 – parallel to the principal axis, and then passes through F after leaving the lens.
object F1 F
The image produced is real, inverted and smaller than the object.
Standard Ray 3 – passes through F1, and then leaves the lens parallel to the principal axis.

59. Lenses and Ray Diagrams
- Predicting where a convex lens will form an image.
Standard Ray 1 – passes through the centre of the lens
Standard Ray 2 – parallel to the principal axis, and then passes through F after leaving the lens.
object F1 F
The image produced is real, inverted and smaller than the object.
Standard Ray 3 – passes through F1, and then leaves the lens parallel to the principal axis.
Only two of the standard rays are required to work out where they go.

60. Lenses and Ray Diagrams
- Predicting where a convex lens will form an image.
Standard Ray 1 – passes through the centre of the lens
Standard Ray 2 – parallel to the principal axis, and then passes through F after leaving the lens.
object F1 F
The image produced is real, inverted and smaller than the object.
Standard Ray 3 – passes through F1, and then leaves the lens parallel to the principal axis.
As the object is moved closer towards the lens, the image becomes bigger and further away.
Only two of the standard rays are required to work out where they go.

61. Uses of Convex Lenses
1. In a projector

62. Uses of Convex Lenses 1. As a magnifying glass F1 F
Object between F1 and lens

63. Uses of Convex Lenses 2. As a magnifying glass F1 F
Object between F1 and lens

64. Uses of Convex Lenses 2. As a magnifying glass F1 F
The rays appear to be coming from a position behind the lens. The image is upright and magnified, and it is called a virtual image because no rays actually meet to form it and the image cannot be formed on a screen. F1 F
The image is virtual, upright and magnified.
Object between F1 and lens

65. Ray Diagram for a Concave Lens
- Predicting where a concave lens will form an image. F

66. Ray Diagram for a Concave Lens
- Predicting where a concave lens will form an image.
object F
The image is virtual, upright and diminished (smaller than the object).

67. LEARNING OBJECTIVES Core
•Describe the formation of an optical image by a plane mirror, and give its characteristics
• Recall and use the law angle of incidence = angle of reflection
Describe an experimental demonstration of the refraction of light
• Use the terminology for the angle of incidence i and angle of refraction r and describe the passage of light through parallel-sided transparent material
• Give the meaning of critical angle
• Describe internal and total internal reflection
Describe the action of a thin converging lens on a beam of light
• Use the terms principal focus and focal length
• Draw ray diagrams for the formation of a real image by a single lens
• Describe the nature of an image using the terms enlarged/same size/diminished and upright/inverted
Supplement
Describe the formation of an optical image by a plane mirror, and give its characteristics
Recall and use the definition of refractive index n in terms of speed
• Recall and use the equation sin I / sin r=n
• Recall and use n = 1 / sin c
• Describe and explain the action of optical fibres particularly in medicine and communications technology
Draw and use ray diagrams for the formation of a virtual image by a single lens • Use and describe the use of a single lens as a magnifying glass • Show understanding of the terms real image and virtual image

68. PHYSICS – Total Internal Reflection and Lenses