1. What would this image look like if you were a fly?!

2. Learning Objectives
By the end of the lesson you should…
To be able to compare the path of light when it enters a thin converging or a thin diverging lens.
To be able to draw simple ray diagrams to show the principle axis, focal point, focal length and focus.
To be able to explain the effect of increasing the thickness of a lens determines its strength.
Two compound eyes each containing approximately 4,000 single pit lenses.

3. Learning Objectives
By the end of this lesson you should be able to…
To be able to compare the path of light when it enters a thin converging or a thin diverging lens.
To be able to draw simple ray diagrams to show the principle axis, focal point, focal length and focus.
To be able to explain the effect of increasing the thickness of a lens determines its strength

4. Continue the 3 rays on each diagram through the lens.
Learning Objectives
By the end of the lesson you should…
To be able to compare the path of light when it enters a thin converging or a thin diverging lens.
To be able to draw simple ray diagrams to show the principle axis, focal point, focal length and focus.
To be able to explain the effect of increasing the thickness of a lens determines its strength.
Continue the 3 rays on each diagram through the lens.

5. Diverging Converging Causes rays to disperse from a central focus.
Learning Objectives
By the end of the lesson you should…
To be able to compare the path of light when it enters a thin converging or a thin diverging lens.
To be able to draw simple ray diagrams to show the principle axis, focal point, focal length and focus.
To be able to explain the effect of increasing the thickness of a lens determines its strength.
Causes rays to disperse from a central focus.
Diverging
Converging
Brings parallel rays into focus (causes them to converge to a point)

6. Will each lens be diverging or converging?
Learning Objectives
By the end of the lesson you should…
To be able to compare the path of light when it enters a thin converging or a thin diverging lens.
To be able to draw simple ray diagrams to show the principle axis, focal point, focal length and focus.
To be able to explain the effect of increasing the thickness of a lens determines its strength.
Will each lens be diverging or converging?

7. What do you notice about the lenses which are diverging / converging?
Learning Objectives
By the end of the lesson you should…
To be able to compare the path of light when it enters a thin converging or a thin diverging lens.
To be able to draw simple ray diagrams to show the principle axis, focal point, focal length and focus.
To be able to explain the effect of increasing the thickness of a lens determines its strength.
What do you notice about the lenses which are diverging / converging?

8. All diverging lenses are wider at the edges than in the center.
Learning Objectives
By the end of the lesson you should…
To be able to compare the path of light when it enters a thin converging or a thin diverging lens.
To be able to draw simple ray diagrams to show the principle axis, focal point, focal length and focus.
To be able to explain the effect of increasing the thickness of a lens determines its strength.
All diverging lenses are wider at the edges than in the center.
All converging lenses are wider in the center than at the edges.

9. Learning Objectives
By the end of the lesson you should…
To be able to compare the path of light when it enters a thin converging or a thin diverging lens.
To be able to draw simple ray diagrams to show the principle axis, focal point, focal length and focus.
To be able to explain the effect of increasing the thickness of a lens determines its strength.
Light travelling through a lens is refracted twice; once when it enters the lens and once when it leaves.
In the case of a thin lens, it is possible to neglect this double bending.

10. Learning Objectives
By the end of the lesson you should…
To be able to compare the path of light when it enters a thin converging or a thin diverging lens.
To be able to draw simple ray diagrams to show the principle axis, focal point, focal length and focus.
To be able to explain the effect of increasing the thickness of a lens determines its strength.
What effect does a convex lens have on parallel rays of light?
Principal Axis
Principal Axis F
Focal point
They will converge to a point which will call the focal point (F). If you put a screen at the focal point you would focus a real image onto the screen.

11. Learning Objectives
By the end of the lesson you should…
To be able to compare the path of light when it enters a thin converging or a thin diverging lens.
To be able to draw simple ray diagrams to show the principle axis, focal point, focal length and focus.
To be able to explain the effect of increasing the thickness of a lens determines its strength.
What effect does a convex lens have on parallel rays of light? f
Principal Axis
Principal Axis F
Focal Length
The distance from the center of the lens to the focal point is called the focal length of the lens (f).

12. Learning Objectives
By the end of the lesson you should…
To be able to compare the path of light when it enters a thin converging or a thin diverging lens.
To be able to draw simple ray diagrams to show the principle axis, focal point, focal length and focus.
To be able to explain the effect of increasing the thickness of a lens determines its strength.

13. What effect does a convex lens have on diverging rays of light?
Learning Objectives
By the end of the lesson you should…
To be able to compare the path of light when it enters a thin converging or a thin diverging lens.
To be able to draw simple ray diagrams to show the principle axis, focal point, focal length and focus.
To be able to explain the effect of increasing the thickness of a lens determines its strength.
What effect does a convex lens have on diverging rays of light?
If a light is placed at the focal point of a convex lens it will produce parallel light

14. What effect does a concave lens have on parallel rays of light?
Learning Objectives
By the end of the lesson you should…
To be able to compare the path of light when it enters a thin converging or a thin diverging lens.
To be able to draw simple ray diagrams to show the principle axis, focal point, focal length and focus.
To be able to explain the effect of increasing the thickness of a lens determines its strength.
What effect does a concave lens have on parallel rays of light?
Principal Axis F
Causes them to disperse, so that they will never converge.
Thus when we talk about the focal point for a diverging lens it is a virtual image and must be found by extending the diverging rays backwards.

15. Learning Objectives
By the end of the lesson you should…
To be able to compare the path of light when it enters a thin converging or a thin diverging lens.
To be able to draw simple ray diagrams to show the principle axis, focal point, focal length and focus.
To be able to explain the effect of increasing the thickness of a lens determines its strength.
What effect does a concave lens have on parallel rays of light? f F
Focal Length
The distance from the centre of the lens to the focal point is called the focal length of the lens (f).

16. Real
Virtual
Which type of image do you need in a projector or camera?

17. F Determining the power of a lens f Power = 1/f
Learning Objectives
By the end of the lesson you should…
To be able to compare the path of light when it enters a thin converging or a thin diverging lens.
To be able to draw simple ray diagrams to show the principle axis, focal point, focal length and focus.
To be able to explain the effect of increasing the thickness of a lens determines its strength.
Determining the power of a lens f
Principal Axis
Principal Axis F
Power = 1/f
Optical power is the ability of a lens to focus an object in a short focal length.

18. Learning Objectives
By the end of the lesson you should…
To be able to compare the path of light when it enters a thin converging or a thin diverging lens.
To be able to draw simple ray diagrams to show the principle axis, focal point, focal length and focus.
To be able to explain the effect of increasing the thickness of a lens determines its strength.
YOUR TASK
Set up a power pack, ray lamp and grating to give you three parallel rays of light
Experiment with the different shaped lenses and sketch the effect they have on the rays, measure some focal lengths for at least three different lenses.
Experiment with pairs of lenses, what effects can you see?
Can you explain quantitatively what happens to the focal length when you use two identical lenses in quick succession.

19. Learning Objectives
By the end of the lesson you should…
To be able to compare the path of light when it enters a thin converging or a thin diverging lens.
To be able to draw simple ray diagrams to show the principle axis, focal point, focal length and focus.
To be able to explain the effect of increasing the thickness of a lens determines its strength.
Experiment: Determine how the focal length changes when the width of the lens is increased.
Questions to answer:
Conclude your experiment, how does the focal length change with the width of the lens.
Does a wider lens have a higher power? Explain your answer
If you were shortsighted do you think the lens in your eye is too wide or too thin?

20. The wider the lens the shorter the focal length
Learning Objectives
By the end of the lesson you should…
To be able to compare the path of light when it enters a thin converging or a thin diverging lens.
To be able to draw simple ray diagrams to show the principle axis, focal point, focal length and focus.
To be able to explain the effect of increasing the thickness of a lens determines its strength.
The wider the lens the shorter the focal length

21. Explain the terms focus and focal length
Explain the difference between a real and virtual image
Draw a simple profile for a converging and diverging lens
Draw a diagram showing short sightedness and explain the problem
Write the formula for determining the power of a lens
Draw a simple diagram showing refraction through a converging lens and label the focus, focal length, lens and rays .

22. Learning Objectives
By the end of this lesson you should be able to…
Review the structure of the eye from biology.
Describe and draw 2 common sight defects and explain how they arise.
Explain how concave and convex lenses of different refractive index and curvature can be used to correct sight defects.

23. The Eye
Blind spot

24. Ciliary muscles
Coloured ring of muscle that controls the amount of light entering the eye.
Eye lens
Attaches the lens to the ciliary muscles
Pupil
Focuses light onto the retina
Suspensory ligaments
Transparent layer that protects the eye and helps to focus light onto the retina.
Cornea
Changes the thickness of the eye lens to change the focal length.
Iris
The light-sensitive cells around the inside of the eye.
Retina
The central hole formed by the iris which allows light through.

25. Sight Defects Review the structure of the eye from biology.
Learning Objectives
By the end of the lesson you should…
Review the structure of the eye from biology.
Describe and draw 2 common sight defects and explain how they arise.
Explain how concave and convex lenses of different refractive index and curvature can be used to correct sight defects.
Sight Defects

26. If you are shortsighted the lens in your eye has too much power!
Learning Objectives
By the end of the lesson you should…
Review the structure of the eye from biology.
Describe and draw 2 common sight defects and explain how they arise.
Explain how concave and convex lenses of different refractive index and curvature can be used to correct sight defects.
If you are shortsighted the lens in your eye has too much power!
The lens is bringing the object into focus before the retina.
How could we solve this problem?

27. Solving Short-sightedness
Learning Objectives
By the end of the lesson you should…
Review the structure of the eye from biology.
Describe and draw 2 common sight defects and explain how they arise.
Explain how concave and convex lenses of different refractive index and curvature can be used to correct sight defects.
Solving Short-sightedness
A simple diverging lens in front of the eye will correct for the higher power of the lens allowing the light to focus on the retina.

28. Learning Objectives
By the end of the lesson you should…
Review the structure of the eye from biology.
Describe and draw 2 common sight defects and explain how they arise.
Explain how concave and convex lenses of different refractive index and curvature can be used to correct sight defects.
Making a lens
Refractive index and curvature of the lens surfaces can be altered to change the power of a lens.
The greater the refractive index, the greater the power
The greater the curvature of the lens surfaces, the greater the power.

29. Long Sighted Review the structure of the eye from biology.
Learning Objectives
By the end of the lesson you should…
Review the structure of the eye from biology.
Describe and draw 2 common sight defects and explain how they arise.
Explain how concave and convex lenses of different refractive index and curvature can be used to correct sight defects.
Long Sighted

30. Learning Objectives
By the end of the lesson you should…
Review the structure of the eye from biology.
Describe and draw 2 common sight defects and explain how they arise.
Explain how concave and convex lenses of different refractive index and curvature can be used to correct sight defects.
How can we tell the (old but much better) Doctor’s glasses aren’t a prescription lens?

31. Learning Objectives
By the end of the lesson you should…
Review the structure of the eye from biology.
Describe and draw 2 common sight defects and explain how they arise.
Explain how concave and convex lenses of different refractive index and curvature can be used to correct sight defects.
The wider the lens the shorter the focal length therefore the higher the power of lens.

32. Learning Objectives
By the end of the lesson you should…
Review the structure of the eye from biology.
Describe and draw 2 common sight defects and explain how they arise.
Explain how concave and convex lenses of different refractive index and curvature can be used to correct sight defects.
When focusing on a distant object the eye requires a long focal length. This can be achieved by relaxing the ciliary muscles.
The far point, the maximum focusing distance of the eye can be considered to be infinity.

33. Learning Objectives
By the end of the lesson you should…
Review the structure of the eye from biology.
Describe and draw 2 common sight defects and explain how they arise.
Explain how concave and convex lenses of different refractive index and curvature can be used to correct sight defects.
When focusing on a nearby object the eye requires a short focal length. This can be achieved by contracting the ciliary muscles.
The near point, the minimum focusing distance of the eye can be considered to be 25cm.

34. LASER Treatment Concentrated beam of light
Learning Objectives
By the end of the lesson you should…
Review the structure of the eye from biology.
Describe and draw 2 common sight defects and explain how they arise.
Explain how concave and convex lenses of different refractive index and curvature can be used to correct sight defects.
LASER Treatment
Concentrated beam of light
High powers can burn through metal
Short Sight defects can be corrected using laser treatment.
A thin layer of the cornea is flattened to reduce the effective power of the cornea and lens.
Why won’t this work for long sight?

35. Long Answer Question Practice
Learning Objectives
By the end of the lesson you should…
Review the structure of the eye from biology.
Describe and draw 2 common sight defects and explain how they arise.
Explain how concave and convex lenses of different refractive index and curvature can be used to correct sight defects.
Long Answer Question Practice
Describe and explain how the eye adapts to different light conditions and to objects at different distances.

36. Name the feature... E A C A = B = C = D = E = Focal Length
Divergent Lens
Focus
Principle Axis
Ray

37. Diverging or Converging Lens

38. Learning Objectives
By the end of this lesson you should be able to…
To be able to draw complex ray diagrams to compare the image formed with the object seen.
To be able to compare the formation of real and virtual images.
To be able to explain the path of light in a magnifying glass and a telescope.

39. Name the feature... E A C A = B = C = D = E = Focal Length
Divergent Lens
Focus
Principle Axis
Ray

40. Diagrams should be drawn to scale
Learning Objectives
By the end of the lesson you should…
To be able to draw complex ray diagrams to compare the image formed with the object seen.
To be able to compare the formation of real and virtual images.
To be able to explain the path of light in a magnifying glass and a telescope.
Drawing Ray Diagrams
Diagrams should be drawn to scale
Draw object as arrow pointing upwards
Construct diagram using two rays

41. To be able to compare the formation of real and virtual images.
Learning Objectives
By the end of the lesson you should…
To be able to draw complex ray diagrams to compare the image formed with the object seen.
To be able to compare the formation of real and virtual images.
To be able to explain the path of light in a magnifying glass and a telescope.

42. To be able to compare the formation of real and virtual images.
Learning Objectives
By the end of the lesson you should…
To be able to draw complex ray diagrams to compare the image formed with the object seen.
To be able to compare the formation of real and virtual images.
To be able to explain the path of light in a magnifying glass and a telescope.

43. Drawing Ray Diagrams 6 Steps... Draw your lens and a principle axis.
Learning Objectives
By the end of the lesson you should…
To be able to draw complex ray diagrams to compare the image formed with the object seen.
To be able to compare the formation of real and virtual images.
To be able to explain the path of light in a magnifying glass and a telescope.
Drawing Ray Diagrams
6 Steps...
Draw your lens and a principle axis.
Mark your Focal point (F) on both sides of the lens using information given.
Draw your image as an arrow up from the principle axis.
Draw one ray going through the centre of the lens, undeflected.
Draw a second ray parallel to the principle axis, deflecting through the Focus once it has passed through the lens.
Look for where the 2 rays meet!

44. Learning Objectives
By the end of the lesson you should…
To be able to draw complex ray diagrams to compare the image formed with the object seen.
To be able to compare the formation of real and virtual images.
To be able to explain the path of light in a magnifying glass and a telescope.
object F F
Focal Length = 9cm

45. Drawing Ray Diagrams 6 Steps... Draw your lens and a principle axis.
Learning Objectives
By the end of the lesson you should…
To be able to draw complex ray diagrams to compare the image formed with the object seen.
To be able to compare the formation of real and virtual images.
To be able to explain the path of light in a magnifying glass and a telescope.
Drawing Ray Diagrams
6 Steps...
Draw your lens and a principle axis.
Mark your Focal point (F) on both sides of the lens using information given.
Draw your image as an arrow up from the principle axis.
Draw one ray going through the centre of the lens, undeflected.
Draw a second ray parallel to the principle axis, deflecting through the Focus once it has passed through the lens.
Look for where the 2 rays meet!

46. How can we describe the image formed?
Learning Objectives
By the end of the lesson you should…
To be able to draw complex ray diagrams to compare the image formed with the object seen.
To be able to compare the formation of real and virtual images.
To be able to explain the path of light in a magnifying glass and a telescope.
object F
image F
How can we describe the image formed?

47. How do we describe our image? Magnified, same size or reduced
Learning Objectives
By the end of the lesson you should…
To be able to draw complex ray diagrams to compare the image formed with the object seen.
To be able to compare the formation of real and virtual images.
To be able to explain the path of light in a magnifying glass and a telescope.
How do we describe our image?
Magnified, same size or reduced
Erect or upside down
Real or virtual

48. Focal length of lens = 4cm Object height = 2cm
Learning Objectives
By the end of the lesson you should…
To be able to draw complex ray diagrams to compare the image formed with the object seen.
To be able to compare the formation of real and virtual images.
To be able to explain the path of light in a magnifying glass and a telescope.
Example Ray Diagram
Focal length of lens = 4cm
Object height = 2cm
Object length (from lens) = 7cm

49. This image is magnified, erect and virtual
Learning Objectives
By the end of the lesson you should…
To be able to draw complex ray diagrams to compare the image formed with the object seen.
To be able to compare the formation of real and virtual images.
To be able to explain the path of light in a magnifying glass and a telescope.
image F F
eye
This image is magnified, erect and virtual

50. Learning Objectives
By the end of the lesson you should…
To be able to compare the path of light when it enters a thin converging or a thin diverging lens.
To be able to draw simple ray diagrams to show the principle axis, focal point, focal length and focus.
To be able to explain the effect of increasing the thickness of a lens determines its strength.
Lens Formula

51. Learning Objectives
By the end of the lesson you should…
To be able to compare the path of light when it enters a thin converging or a thin diverging lens.
To be able to draw simple ray diagrams to show the principle axis, focal point, focal length and focus.
To be able to explain the effect of increasing the thickness of a lens determines its strength.

52. Work through the ‘More Ray Diagrams’ worksheet
Learning Objectives
By the end of the lesson you should…
To be able to draw complex ray diagrams to compare the image formed with the object seen.
To be able to compare the formation of real and virtual images.
To be able to explain the path of light in a magnifying glass and a telescope.
Work through the ‘More Ray Diagrams’ worksheet

53. Focussing a Camera

54. Real or Virtual? Mirror Projector Binoculars Magnifying glass
Learning Objectives
By the end of the lesson you should…
To be able to draw complex ray diagrams to compare the image formed with the object seen.
To be able to compare the formation of real and virtual images.
To be able to explain the path of light in a magnifying glass and a telescope.
Real or Virtual?
Mirror
Projector
Binoculars
Magnifying glass
Microscope
Camera
Eye
Remember with a virtual image the rays will never really converge but it will appear that the image you are seeing converges behind the lens.