PHY205H1F Summer Physics of Everyday Life Class 10: Colour , Optics

1. PHY205H1F Summer Physics of Everyday LifeClass 10: Colour, Optics Virtual Image Formation Image Reversal Concave Mirrors Diffuse Reflection Refraction Total Internal Reflection Lenses Color in Our World Mixing Colored Light Why the Sky Is Blue Why Sunsets Are Red Law of Reflection

2. Recall from Chapters 25 and 26… • A changing electric field creates a field, which then changes in just the right way to recreate the field, which then changes in just the right way to again recreate the field, and so on. • This is an electromagnetic wave.

3. Why Sunsets Are Red CHECK YOUR NEIGHBOR What property of a light wave mainly determines its colour? • Its frequency • Its amplitude • Its timbre • A mix of all of the above

4. Color Color we see depends on frequency of light. Low Frequency, Long High Frequency, Short

5. Selective Reflection A red ball seen under white light. Only is reflected, other colors are absorbed. A red ball seen under green light. There is no source of red light to reflect! A red ball seen under red light.

6. Mixing Colored Light The spectrum of sunlight is a graph of brightness versus frequency. Somehow, this mix looks “ ” to us.

7. Why Sunsets Are Red CHECK YOUR NEIGHBOR A beam of white light, when shone through a prism, will end up many different colours.What will happen if a green laser is shone through a prism? • It will spread into a small range of colours. • It will change to a single colour other than green. • It will stay green.

8. Rhodopsin is a transmembrane protein complex. Rods and cones contain stacks of membranes. Opsin (protein component) Retinal (pigment) 0.5 µm Cone Rod Rhodopsin Light Light The retinal molecule inside rhodopsin changes shape when retinal absorbs light. trans conformation (activated) cis conformation (inactive) Opsin Light Opsin Slide courtesy of Ross Koning, Biology Department, Eastern Connecticut State University http://plantphys.info/sciencematters/vision.ppt

9. Response Curves for the three types of cones in the retina of the human eye. Slide from http://hyperphysics.phy-astr.gsu.edu/hbase/vision/colcon.html

10. Use both eyes, stare at area shown in blue for 15 seconds or so

11. What do you see on this blank white slide? Blink if needed! This is called an “after image” Does it move around as you move your gaze?

12. Use both eyes, stare at the parrot’s eye for 15 seconds or so Stare at the bird’s eye for 10 seconds without tilting your head.

13. Bird Was Red What colour is the afterimage bird? orange green blue yellow None of the above

14. Use both eyes, stare at the parrot’s eye for 15 seconds or so Stare at the bird’s eye for 10 seconds without tilting your head.

15. Bird Was Green What colour is the afterimage bird? red orange blue violet None of the above

16. Use both eyes, stare at the parrot’s eye for 20 seconds or so Stare at the bird’s eye for 10 seconds without tilting your head.

17. Bird Was Blue What colour is the afterimage bird? red orange yellow green None of the above

18. Additive Primary Colours (light bulbs)and Subtractive Primary Colours (ink)

19. Discussion Question • Why is this square red? • The light bulbs in the projector emit light with blue frequencies • The light bulbs in the projector emit light with green frequencies • The light bulbs in the projector emit light with red frequencies • Both A and B

20. Discussion Question • Why is the red folder in Harlow’s hand red? • The pigments in the paper absorb light with blue frequencies • The pigments in the paper absorb light with green frequencies • The pigments in the paper absorb light with red frequencies • Both A and B

22. Discussion Question : Using the colour wheel.. • When the colour yellow is seen on the screen of your computer, what are the lights being activated in that region of your screen? • Mainly yellow • Blue and red • Green and yellow • Red and green

23. Discussion Question : Using the colour wheel.. • If an object is blue, which of the coloured lights below would make the object appear most black? • blue • cyan • yellow • magenta

24. Discussion Question : Using the colour wheel.. • If an object is red, which of the coloured lights below would make the object appear not appear red? • red • orange • white • cyan

25. Why the Sky Is Blue For small scattering particles, like nitrogen or oxygen molecules, frequency blue light is scattered much more readily than lower frequency red light.

26. Why the Sky Is Blue

27. Why Sunsets Are Red CHECK YOUR NEIGHBOUR If molecules in the sky scattered orange light instead of blue light, the sky would be A. orange. • yellow. • green. • blue.

28. Doppler Shift for Light • When a light source is moving from you, the spectrum is shifted toward the red. • When a light source is moving you, the spectrum is shifted toward the blue.

29. Doppler Shift for Light • The Doppler shift can be observed with carefully obtained spectra of very fast moving objects like stars • There is a slight shift in “absorption lines”

30. Why Sunsets Are Red Light that is least scattered is light of low frequencies, which best travel straight through air.

31. Why Sunsets Are Red CHECK YOUR NEIGHBOUR If molecules in the sky scattered orange light instead of blue light, sunsets would be A. orange. • yellow. • green. • blue.

32. Why Clouds Are White • Clouds are clusters of various sizes of water droplets

33. Why Clouds Are White Size of clusters determines scattered cloud color. • Tiny clusters produce bluish clouds. • Slightly large clusters produce greenish clouds. • Larger clusters produce reddish clouds. • Overall result is white clouds. • Slightly larger clusters produce a deep gray. • Still larger clusters produce raindrops.

34. Why Sunsets Are Red CHECK YOUR NEIGHBOR What does a white sky indicate? • The atmosphere has mostly particles smaller than the wavelength of light • The atmosphere has mostly particles larger than the wavelength of light • The atmosphere has a mixture of particle sizes • The atmosphere has a lot of water vapour • The atmosphere is filled with pollutants.

35. Law of Reflection The angle of reflection equals the angle of incidence.

36. A dentist uses a mirror to look at the back of a second molar (A). • Next, she wishes to look at the back of a lateral incisor (B), which is 90° away. • By what angle should she rotate her mirror? Mirror A B A. 90° B. 45° C. 180°

37. Virtual Image Formation No light rays actually pass through or even near the image, so it is “virtual”.

38. Two plane mirrors form a right angle. How many images of the ball can the observer see in the mirrors? 1 2 3 4

39. Which picture is most likely a mirror image of Harlow? A B D C

40. Virtual Image Formation • Alice looks at Bob’s image a mirror and sees he has a red shoe on the foot to Alice’s left. • Then she asks Bob to turn and face her, so she can compare the image to what Bob looks like in real life. • Bob takes a couple of steps forward, turns around and faces Alice. • Alice notes that the red shoe is now on the foot on the . • Alice concludes: “Mirrors reverse left and right, not up and down.” Is this true? Can you see any flaws in Alice’s reasoning? real mirror

41. Virtual Image Formation Bob in Mirror Bob turns to face Alice • Bob chooses to rotate around a vertical axis, and therefore he looks flipped left-to-right. • But if Bob wants to turn to face Alice, is there any other way to do it?

42. What really happens is the image is reversed front-to-back

43. Refraction When light bends in going obliquely from one medium to another, we call this process refraction.

44. Cause of Refraction • Bending of light when it passes from one medium to another • Caused by change in of light

45. A soldier wants to get from point 1 to Point 2 in the shortest amount of time. Marching through mud is much slower than marching on dry land. Which might be the best path? 1 Dry Land C A B Mud Dry Land 2

46. Refraction Light travels in glass than in air, so it minimizes the time it spends in the glass.

47. air water A fish swims below the surface of the water. An observer sees the fish at: A. a greater depth than it really is. B. its true depth. C. a smaller depth than it really is.

48. Dispersion • Process of separation of light into colors arranged by frequency • Components of white light are dispersed in a prism (and in a diffraction grating).

49. Rainbows Rainbows are a result of dispersion by many drops. • Dispersion of light by a single drop

50. Rainbows Antisun Radius of circle is about 41°