1. AQA GCSE 3-2A Light
GCSE Physics pages 234 to 253
April 10th 2010

2. AQA GCSE Specification
OPTICS
13.4 What do mirrors and lenses do to light?
Using skills, knowledge and understanding of how science works:
• to construct ray diagrams to show the formation of images by plane, convex and concave mirrors
• to construct ray diagrams to show the formation of images by diverging lenses and converging lenses
• to explain the use of a converging lens as a magnifying glass and in a camera
• to calculate the magnification produced by a lens or mirror using the formula:
magnification = image height / object height
Skills, knowledge and understanding of how science works set in the context of:
• The normal is a construction-line perpendicular to the reflecting/refracting surface at the point of incidence.
• The angle of incidence is equal to the angle of reflection.
• The nature of an image is defined by its size relative to the object, whether it is upright or inverted relative to the object and whether it is real or virtual.
• The nature of the image produced by a plane mirror.
• The nature of the image produced by a convex mirror.
• The nature of the image produced by a concave mirror for an object placed at different distances from the lens.
• Refraction at an interface.
• Refraction by a prism.
• The nature of the image produced by a diverging lens.
• The nature of the image produced by a converging lens for an object placed at different distances from the lens.
• The use of a converging lens in a camera to produce an image of an object on a detecting device (eg film).

3. Reflection

4. Law of Reflection
The angle of incidence (i) is equal to the angle of reflection (r)
Note: Both angles are measured with respect to the ‘normal’. This is a construction line that is perpendicular to the reflecting surface at the point of incidence.
mirror
angle of
incidence, i
incident ray
normal
reflected ray
angle of
reflection, r

5. The image formed by a plane mirror
object
image
plane mirror
construction lines (virtual light rays)
normals
The image produced by the plane mirror is:
The same size as the object
The same distance behind the mirror as the object is in front
Upright (the same way up as the object)
Back-to-front compared with the object (lateral inversion)
Virtual

6. Real and virtual images
REAL images are formed where light rays cross after reflection by a mirror or refraction by a lens.
Real images can be cast onto a screen.
Example: A projector image
VIRTUAL images are formed where light rays only appear to come from.
A virtual image cannot be cast onto a screen.
Example: The image formed by a plane mirror

7. Choose appropriate words to fill in the gaps below:
The law of reflection states that the angle of __________ is always _______ to the angle of incidence.
Both angles are measured relative to the _________, a line that is at _______ degrees to the reflecting surface at the point of reflection.
A plane mirror forms a _______ image which is unlike a _____ image in that it cannot be cast onto a screen. The image in a plane mirror is also the same ______ and the same way up as the object.
reflection
equal
normal
ninety
virtual
real
size
WORD SELECTION:
normal
virtual
size
reflection
real
equal
ninety

8. Simulations Optical illusions - by eChalk BBC KS3 Bitesize Revision:
KS3 Light Contents Page
What is light?
Seeing
Test bite on KS3 Light
Law of Reflection - NTNU - features a movable plane mirror
Reflection in a plane mirror - eChalk
Balloon blasting game - eChalk
Height of mirror and image seen - NTNU
Virtual image formation - eChalk
Image formed by a plane mirror - NTNU
Reflection and images from two mirrors at 90 degrees to each other - NTNU
Law of Reflection - Crocodile Clip Presentation
Reflection & Scattering

9. Reflection Notes questions from pages 234 & 235
Explain how convex and concave mirrors differ from plane mirrors.
Copy Figure 2 on page 235 and state what is meant by (a) the law of reflection and (b) the ‘normal’ line.
Copy Figure 1(b) on page 234 and use it to explain what is meant by a ‘virtual’ image.
What is a real image? Give two examples.
Copy and answer questions (a), (b) and (c) on pages 234 and 235.
Copy the ‘Key points’ table on page 235.
Answer the summary questions on page 235.

10. Reflection ANSWERS In text questions: 1.0 m (i) 20o (ii) 40o Virtual
Summary questions:

11. A concave mirror is like the inside of a spoon.
principal focus
principal axis O C
centre of curvature
radius of curvature, r
focal length, f
centre
of the mirror

12. Convex mirror A convex mirror is like the outside of a spoon.
principal focus
principal axis O
centre of curvature C
radius of curvature, r
focal length, f

13. Mirror definitions
The principal axis is a construction line that is perpendicular to and passes through the centre of the mirror, O.
The principal focus, F is the point through which all rays travelling parallel to the principal axis before reflection pass through or appear to come from after reflection.
The focal length, f is the distance from the centre of the mirror, O to the principal focus, F.
The centre of curvature, C is the centre of the circle of which the surface of the mirror is a part.
The radius of curvature, r is the distance along the principal axis between the centre of the mirror, O and the centre of curvature and equal to TWICE the focal length, f of the mirror.

14. Standard rays – concave mirror
(a) Rays incident parallel to the principal axis pass through the principal focus after reflection.
concave mirror F
principal axis

15. (b) Rays passing through the centre of curvature before reflection are reflected back along their initial path. F
principal axis C
centre of curvature

16. (c) Rays striking the centre of the mirror are reflected as if the mirror was flat.

17. Concave mirror images
1. Object more than the radius of curvature away from the mirror. F C O
object
image
Use: Satellite receiver (with microwaves)
The image formed is:
Smaller than the object (diminished)
Between F and C
Inverted (upside down)
Real

18. 2. Object between F and C F C O
object
image
Use: Satellite transmitter (with microwaves)
The image formed is:
Larger than the object (magnified)
Beyond C
Inverted
Real

19. 3. Object nearer than the principal focus
image
observer
Use: Makeup and shaving mirrors
The image formed is:
Larger than the object
On the other side of the mirror from the object
Upright
Virtual

20. Standard rays – convex mirror
(a) Rays incident parallel to the principal axis appear to come from the principal focus after reflection.
convex mirror
principal axis F

21. (b) Rays heading for the centre of curvature before reflection are reflected back along their initial paths. C
convex mirror
principal axis F

22. (c) Rays striking the centre of the mirror are reflected as if the mirror was flat.

23. Convex mirror images Objects at all distances from a convex mirror
observer
Use: Security mirrors
The image formed is:
Smaller than the object
On the other side of the mirror from the object
Upright
Virtual
Convex mirrors give a wide field of view

24. Magnification magnification = image height object height Question:
Calculate the magnification if a mirror produces an image of 40cm from an 8cm sized object.
magnification = image height / object height
= 40cm / 8cm
magnification = 5 x

25. Complete: Answers 8 x 15 cm 5 cm 3 x object height image height
magnification
3 cm
24 cm
45 cm
3 x
20 cm
0.25 x
300 mm
0.10 m
8 x
15 cm
5 cm
3 x

26. Choose appropriate words to fill in the gaps below:
There are two types of curved mirror, __________ and convex. Concave mirrors look like the ________ of a spoon.
Concave mirrors __________ light parallel to the principal axis so that all the rays pass through the __________ focus. Makeup mirrors can be concave in order to provide a __________ view of the face.
Light is diverged by _________ mirrors. These always produce _______ images and are used to provide a wide field of view which is especially useful for ____ rear view mirrors.
concave
inside
converge
principal
magnified
convex
virtual
car
WORD SELECTION:
converge
magnified
concave
principal
car
convex
inside
virtual

27. Simulations Lens / mirror effect on a beam of light - NTNU
Tiger image formation by a plane or curved mirror - NTNU
Mirage of pig formed by a concave mirror - includes UTube clip - NTNU
Curved mirror images / ray diagrams - NTNU

28. Curved mirrors Notes questions from pages 236 & 237
By referring to a copy of Figure 2 on page 236 define what is meant by (a) the principle focus and (b) the focal length of a concave mirror.
Under headings ‘Object beyond principle focus’ and ‘Object between focal point and the mirror’ copy Figures 3 and 4 on page 237 and describe the type of image formed in each case.
Define what is meant by magnification.
Copy Figure 5a on page 237 and describe the type of image formed.
Copy the Key Points on page 237.
Copy and answer questions (b) and (c) on pages 236 and 237.
Answer the summary questions on page 237.

29. Curved mirrors ANSWERS
In text questions:
(b) (c) Upright, magnified, virtual.
Summary questions:
1. (a) Real, inverted, in front. (b) Virtual, upright, behind.
(b) The image is virtual, upright and twice as large as the object.

30. Refraction

31. Refraction occurs when a wave changes speed as it passes from one region to another.
This speed change usually causes the wave to change direction.
Water waves slow down as they pass over from a deeper to a shallower region.
Light slows down as it passes from air into glass, perspex or water.

32. Refraction of light at a plane surface
(a) Less to more optical dense transition (e.g. air to glass)
angle of incidence
normal
AIR GLASS
angle of refraction
Light bends TOWARDS the normal.
The angle of refraction is LESS than the angle of incidence.

33. Light bends AWAY FROM the normal.
(b) More to less optical dense transition (e.g. water to air)
angle of incidence
normal
WATER AIR
angle of refraction
Light bends AWAY FROM the normal.
The angle of refraction is GREATER than the angle of incidence.

34. Refraction experiment
Typical results:
angle of incidence / °
angle of refraction / °
deviation / ° 15 10 5 30 19 11 45 28 17 60 35 25 75 40
No deviation occurs when the angle of incidence is zero.
Increasing the angle of incidence increases the deviation.

35. Why a pool appears shallow
observer
normals
object at the bottom of a pool
AIR
WATER
image

36. Complete the paths of the RED light rays:B C D E F

37. Dispersion
A prism splits the colours of white light into the spectrum.
This is called dispersion.
Violet light deviates the most,
red the least.
prism
white
light
spectrum

38. Choose appropriate words to fill in the gaps below:
Refraction occurs when a wave changes ______ as it crosses the boundary between two regions. The _________ of the wave also usually changes.
Light rays deviate ________ the normal when they pass from less dense air to more dense _________. The greater the angle of incidence the greater is the _________.
Different ______ of light deviate by different amounts. Violet deviates the _____. A prism can be used to split the colours of white light into a spectrum. This is called _________.
speed
direction
towards
perspex
deviation
colours
most
dispersion
WORD SELECTION:
towards
deviation
most
dispersion
direction
perspex
speed
colours

39. Simulations Refraction - Powerpoint presentation by KT
Light Refraction - Fendt
Reflection & Refraction at a boundary - NTNU
Refraction animation - NTNU - Does not show TIR effect
Law of Refraction - Crocodile Clip Presentation
Prism - non dispersive reflections and refractions - NTNU
Prism/Lens - non dispersive refraction and reflections - NTNU
BBC KS3 Bitesize Revision:
Refraction
Light moving from water to air - NTNU
Where is the fish? - refraction by water - NTNU
The appearance of an object under water / ray diagram - NTNU
How a fish sees the world - NTNU
Fibre optic reflection - NTNU
BBC Bitesize Revision:
Optical fibres
Dispersion - Powerpoint presentation by KT
Dispersion of light using a prism - NTNU - prism apex angle can be changed
Prism showing light dispersion for different colours - Explore Science
Dispersion - Crocodile Clip Presentation
Sequential Puzzle on Colour Spectrum order- by KT  - Microsoft WORD
Prism - multishape prism and single light ray - no extra reflections - netfirms
Dispersion

40. Refraction Notes questions from pages 238 & 239
Copy Figure 1 on page 238 and use it to explain what is meant by refraction. Also copy the two bullet points to the right of Figure 1.
Copy Figure 2 on page 238 and use it to explain the cause of refraction.
Explain how the speed of light is related to the refraction of light.
Draw a diagram and use it to explain why a swimming pool appears to be shallower than it actually is.
Explain, with the aid of a diagram, how a prism can be used to split white light into its component colours. How does this experiment indicate that red light travels faster than blue light through glass?
Copy and answer questions (a), (b), (c) and (d) on pages 238 and 239.
Copy the ‘Key points’ table on page 239.
Answer the summary questions on page 239.

41. Refraction ANSWERS In text questions: Yes
The top part moves faster than the lower part of the wave so the wave topples over at the top.
The same.
(i) Slower (ii) Faster
Summary questions:
1. (a) Decreases, towards. (b) Increases, away from. (c) Decreases
(b) White light consists of all the colours of the spectrum. The beam is split into these colours because each colour is refracted slightly differently, owing to their different speeds in glass.

42. Lenses

43. Converging lens With glass and plastic lenses a converging lens
has a convex shape.
Converging lens with a parallel beam of light F
principal focus
centre
of the lens
converging lens
principal axis O
focal length, f

44. Diverging lens
With glass and plastic lenses a diverging lens has a concave shape.
Diverging lens with a parallel beam of light O
diverging lens
principal axis F
principal focus
focal length, f

45. Lens definitions
The principal axis is a construction line that is perpendicular to and passes through the centre of the lens.
The principal focus, F is the point through which all rays travelling parallel to the principal axis before refraction pass through or appear to come from after refraction.
The focal length, f is the distance from the centre of the lens, O to the principal focus, F.

46. Standard rays – converging lens
(a) Rays incident parallel to the principal axis pass through the principal focus after refraction. F
principal focus
principal axis

47. (b) Rays passing through the centre of the lens are not deviated.

48. (c) Rays passing through the principal focus before refraction are refracted parallel to the principal axis. F
principal axis

49. Converging lens images
1. Object more than twice the focal length distant from a converging lens F 2F O
object
image
Uses: Camera and Eye
The image formed is:
Smaller than the object
(diminished)
Between the F and 2F
Inverted (upside down)
Real

50. 2. Object between F and 2F F 2F
object
image
Use: Projector
The image formed is:
Larger than the object
(magnified)
Beyond 2F
Inverted
Real

51. 3. Object nearer than the principal focus
image
object
observer
Uses: Magnifying glass
The image formed is:
Larger than the object
On the same side of the lens as the object
Upright
Virtual

52. Standard rays – diverging lens
(a) Rays incident parallel to the principal axis appear to come from the principal focus after refraction.
diverging lens
principal axis F

53. (b) Rays passing through the centre of the lens are not deviated.

54. (c) Rays heading for the principal focus before refraction are deviated parallel to the principal axis. O F
principal axis

55. Diverging lens images Objects at all distances from a diverging lens
observer
object
image
Use: Correction of short sight
The image formed is:
Smaller than the object
On the same side of the lens as the object
Upright
Virtual

56. The Camera
The camera uses a converging lens to produce an image on a light detecting surface such as a CCD (Charge Coupled Device) chip or photographic film.

57. The image produced is therefore: diminished, inverted and real.
In most cases the subject (object) is well more than twice the focal length of the lens away from the camera.
The image produced is therefore:
diminished, inverted and real. F 2F
subject (object)
image produced on CCD or film

58. Structure of a simple camera
CCD or film
shutter
lens
aperture
Focussing is achieved by moving the lens away from or towards the light detector. The further the subject is away from the camera the closer the lens is moved towards the CCD / film.
The amount of light reaching the light detector is controlled by adjusting the size of the ‘stop’ aperture and the length of time that the shutter opens.

59. Choose appropriate words to fill in the gaps below:
Lenses work by the process of _________. A converging lens is made by using a _______ shaped piece of glass or perspex.
A magnifying glass requires the object to be placed _______ than its focal length. The image formed is _______.
A projection lens produces a __________ and inverted image whereas a camera lens normally produces a _________ image. In both cases the image is ______.
Diverging lenses are used to correct ______sight.
refraction
convex
nearer
virtual
magnified
diminished
real
short
WORD SELECTION:
convex
magnified
short
refraction
nearer
real
virtual
diminished

60. Simulations
Geometric Optics with Lenses - PhET - How does a lens form an image? See how light rays are refracted by a lens. Watch how the image changes when you adjust the focal length of the lens, move the object, move the lens, or move the screen.
Prism/Lens - no dispersive refraction and reflections - NTNU
Lens images / ray diagrams - NTNU
How an image is formed by a convex lens / effect of stopping down lens - NTNU
Lens / mirror effect on a beam of light - NTNU

61. Lenses Notes questions from pages 240 & 241 also uses pages 252 and 253
Copy the diagram for Exam Style Question 2(a) on page 252 and use it to explain what is meant by the principle focus is of a converging lens.
Copy the diagram for Exam Style Question 2(b) on page 253 and use it to explain what is meant by the principle focus is of a diverging lens.
For both types of lens define what is meant by focal length.
Describe, with the aid of diagrams, how the image formed by a converging lens changes as the distance to the object decreases.
Copy and answer questions (a), (b) and (c) on pages 240 and 241.
Copy the ‘Key points’ table on page 241.
Answer the summary questions on page 241.

62. Lenses ANSWERS In text questions: A 5 cm focal length lens Inverted
To make it appear much larger so any flaws can be seen.
Summary questions:
(a) Converging, real.
(b) Diverging, virtual.
2. (a) Upright, enlarged and virtual.
(b) (i) Inverted, enlarged and virtual.
(ii) The slide must be moved towards the screen.
(c) The image real, inverted and enlarged. Magnification = 3.

63. Using lenses Notes questions from pages 242 & 243
Copy Figure 1 on page 242 with all of the labels and explain the rules for drawing the three rays shown.
Draw Figure 2 on page 242 and explain how the lens of a camera has to be adjusted to cope with a range of object distances.
Explain with the aid of Figure 3 on page 243 how a magnifying glass produces an image.
Explain with the aid of Figure 4 on page 243 how a concave lens produces an image.
Copy and answer questions (a), (b), (c) and (d) on pages 242 and 243.
Copy the ‘Key points’ table on page 243.
Answer the summary questions on page 243.

64. Using lenses ANSWERS Summary questions: In text questions:
(b) Towards the object.
(c) To inspect objects in detail.
(d) The image is always smaller than the object.

65. Light and sound issues Notes questions from pages 250 & 251
Answer questions 3(a) and 3(b) and on page 251.

66. Light and sound issues ANSWERS
(a) About 166 hours.
(b) The data is permanently stored on the disc.

67. How Science Works ANSWERS
Either greater accuracy or precision.
Millimetres
The range of the dependent variable was to
The mean of the dependent variable was ; reasonably 1.52.
Jenny was using crown glass.