Optics and waves

1. Optics and waves What do you think the word optic means? Can you think of any words which include optic? What do you think waves are? Can you give examples of waves

2. Optics • the scientific study of sight and the behaviour of light, or the properties of transmission and deflection of other forms of radiation

3. Waves • physics an oscillation propagated through a medium or space such that energy is periodically interchanged between two kinds of disturbance.

4. What do you need to help you see objects? • What part of our body helps us see the light? • Eye activity

5. Light is a type of radiation.What else do you know about light? Where does all the light on the Earth come from? How does the light get here?

6. Lesson Starter • In physics what does the term optic refer to? • What do humans require to allow us to see an object? • What is the source of light on earth? • In what direction does light travel?

7. What is the speed of light? • 3.0 x 108 m/s (300,000,000m/s) • It takes 8 minutes for the light from the sun to reach the earth What is the speed of sound? • 340m/s

8. Speed of light/ Speed of sound

9. Light Light is a type of energy Light travels in waves which transfer energy Light always travels in a straight line

10. What Colour is Light?

11. Starter • What happens to light when it travels into glass or water? • What are the colours of the visible light spectrum (rainbow)? • Name three applications of lenses and prisms.

12. Lesson Starter • What are the colours of the visible light spectrum? • What is the speed of light? • In what direction does light travel? • What happens to light when it passes from one material to a different material?

13. Refraction of Light Refraction of light occurs when the light passes from one material into a different material e.g. glass ￫ air or air ￫glass A rainbow is produced when sunlight passes through the water vapour produced in a rain shower. The behaviour of light passing through glass or perspex can be used in many applications. Lenses and Prisms are normally used in these applications.

14. Applications of Optics (Lenses and Prisms)

15. Refraction of Light – Change of Speed • When light travels from air to a denser material such as glass or perspex, the light slows down. • When the light travels from glass to air, the light speeds up. • The speed of light in air is 300 million metres per second • The speed of light in glass is about 200 million metres per second. Resource: Animations ￫ ‘Refraction of Waves’

16. Practical – Bending of Light due to Refraction • Place rectangular perspex block on a piece of paper and draw around its outline. Mark the normal line. 2. Using a single slit, point the light box so that a single ray hits the block at an angle as shown: 3. Draw the light ray entering and leaving the block. Use arrows to show the direction of the ray. 4. Remove the block and draw a straight line between the light entering and leaving the block. 5. Measure the angles of incidence and refraction.

17. Air Glass Normal r Normal i Angles of Incidence and Refraction • The angle of incidence is the angle between the incident ray and the normal (not the surface!). • The angle of refraction is the angle between the refracted ray and the normal.

18. Direction of Light through Glass • When light travels from air to glass it bends towards the normal. • When light travels from glass to air it bends away from normal. Air Glass The normal is an imaginary line at right angles to the glass surface. Normal r Normal i

19. Why is light refracted when it hits a denser material? Think about what happens to a car when it moves from tarmac on to a mud puddle

20. Lesson Starter • What happens to light when it travels from glass into air? • What name do give to the imaginary line that is drawn perpendicular to the surface of an object in ray diagrams? • Angles in ray diagrams are always measured between which two lines?

21. Lesson StarterComplete this ray diagram Air Glass

22. Air Glass Normal r Normal i Angles of Incidence and Refraction • The angle of incidence is the angle between the incident ray and the normal (not the surface!). • The angle of refraction is the angle between the refracted ray and the normal.

23. Worksheet – Refraction of Light through glass blocks.

24. Lesson StarterComplete this ray diagram Air • List the seven colours of visible light • What do you have to pass visible light through in order to see these colours?

25. Visible Light • Visible light is the type of radiation we are most familiar with. • Visible light consists of the seven colours of the rainbow. R – Red O- Orange Y – Yellow G – Green B – Blue I – Indigo V - Violet • The white light we see from a bulb or the sun is made up of all these colours Roy G Biv video http://www.youtube.com/watch?v=Gf33ueRXMzQ

26. White Light Through A Prism • When we shine white light through a prism, the light bends due to refraction. • The different colours of light bend by different degrees • The colours are therefore split as shown. • This range (spread) of colours is called the Visible Spectrum

27. Visible Light Bill Nye Colours of Light video: http://www.youtube.com/watch?v=gtgBHsSzCPE

28. Lesson StarterComplete this ray diagram • Explain why light splits into all the colours of the visible spectrum when it goes through the prism. • What colour bends the least? • What colour bends the most?

29. Learning Intention • To learn what happens to light as it passes through convex and concave lenses. Success Criteria • I can make a diagram of light passing through a concave lens • I can make a diagram of light passing through a convex lens

30. Convex Lens Concave Lens Lenses • A lens is a piece of transparent material shaped a certain way. • The two types of lens are:

31. Ray Box Lenses - Practical • Select the Convex Lens from the Optics Kit. Position lens on white paper and draw round its outline. 2. Switch on Ray Box and direct parallel rays as shown: 3. Trace over the rays before and after they leave the lens. Mark arrows on the lines to show the direction of the rays. 4. Repeat steps 1-3 for the Concave Lens.

32. Lesson Starter Complete this ray diagram • What are the name of the two types of lenses we looked at in the previous lesson? • Draw these two lenses, then add in what would happen to the three rays of light when they pass through

33. Lesson Starter • Name the two types of lenses • How many light beams do we pass through the lenses? • What happens to the light as it travels through a concave lens? • What happens to the light as it travels through a convex lens?

34. Focal Point Convex Lens - Summary A Convex Lens is also known as a Converging Lens as it brings light to a focus. Focal Length • The point where the rays meet (converge) is called the Focal Point. • The Focal Length of a lens is the distance between the lens and the focal point.

35. Concave Lens - Summary A Concave Lens is also known as a Diverging Lens as it separates parallel light.

36. Sheet Of Paper Far Away Object Lens Window • Hold a convex lens near the classroom window. • Hold a sheet of paper close to the lens until image of far away object can be seen – What do you notice about image? 3. Adjust the position of the paper until you get the sharpest image – This is the image in focus. • Accurately measure the distance between the lens and the paper – This is the focal length of the lens.

37. Far Away Object Lens Window Practical – Focal Length of Lenses

38. Object Image Focused Images When light reflected from an object passes through a lens or combination of lenses an image of the object can be formed: The image of a far away object through a convex lens is upside down (inverted) and smaller (diminished).

39. Lesson Starter • When you use a lens to focus an image on a piece of paper, describe how the image will appear? • List as many parts of the human eye as you can. • What type of lens (concave or convex) do you think is found in the human eye?

40. Mr. Gallagher’s Retina Main Parts of the Human Eye The Human Eye

41. Lesson Starter • Draw a diagram of a normal human eye showing the lens, the light rays and the image focussing on a retina. • What are the two common conditions called in humans when an image is not focussed clearly.

42. Images on the Retina – Normal Sight The lens in our eyes will bring light to a focus on the retina at the back of the eye, which acts like a film camera or screen. Retina The image on our retina is upside down (inverted). Our brain turns the image the correct way up to appear normal. http://www.twigonglow.com/films/how-we-see-part-1-eyes-944/

43. Short Sight • Short sighted people cannot see far away objects clearly • Their eyes will focus the light in front of the retina. This means that the image on the retina is out of focus and blurred. Focus is in front of retina • Short sight affects about 25% of people in the UK.

44. Images in Focus The picture on the left is a typical view a short sighted person would get when viewing far away objects – it is blurred. The picture on the right is the image a normal sighted person would get – it is sharp with lots of detail.

45. Long Sight • Long Sighted people cannot see close up objects clearly • Their eyes will focus the light behind the retina. This means that the image on the retina is out of focus and blurred. Focus is behind retina

46. Correcting Short Sight Blurred Image on Retina Sharp Image on Retina Concave Lens

47. Correcting Long Sight Blurred Image on Retina Sharp Image on Retina

48. Lesson Starter • Draw an eye, including the three light rays of a person who is short sighted. • What type of lens would be used to correct this? • Draw an eye, including the three light rays of a person who is long sighted. • What type of lens would be used to correct this?

49. Telescopes • The first telescope was designed exactly 400 years ago (1609). • The Hubble Telescope orbits earth and is positioned above the atmosphere (which absorbs the light which reaches our planet). Q. Why can’t we see far away objects clearly? • Because they don’t take up much space on your eye’s screen (retina).

50. Objective Lens • A basic design of a telescope, using two convex lenses, is shown below: Eyepiece Lens • The Objective Lens takes a lot of light from a far away object and brings it to a focus. • The Eyepiece Lens takes this small image and spreads it out (magnifies it) so that it takes up a large part of the retina. • This makes the object look big as it is spread out on our eye!