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

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. What property of a light wave mainly determines its colour?
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 0.4 𝜇m 0.7 𝜇m 𝑓 𝜆 Color we see depends on frequency of light.
High Frequency,
Short
Low Frequency,
Long 𝜆

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

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

7. It will spread into a small range of colours.
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. Rods and cones contain stacks of membranes.
Rhodopsin is a transmembrane protein complex.
Opsin (protein component)
Retinal (pigment)
Cone
Rod
0.5 µm
Rhodopsin
Light
Light
The retinal molecule inside rhodopsin changes shape when retinal absorbs light.
trans conformation (activated)
cis conformation (inactive)
Opsin
Opsin
Light
Slide courtesy of Ross Koning, Biology Department, Eastern Connecticut State University 8

9. Response Curves for the three types of cones in the retina of the human eye.
Slide from

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
𝑓𝑟𝑒𝑞𝑢𝑒𝑛𝑐𝑦

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. What does a white sky indicate?
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
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?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. 1 Dry Land C A B Mud Dry Land 2
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°

51. Double-rainbow
The second rainbow has blue on the top, and a radius of about 53°

52. Total Internal Reflection
Total reflection of light traveling within a medium that strikes the boundary of another medium at an angle at, or greater than, the angle

53. Discussion Question
Light waves with speed v1 are incident upon the flat surface of a material in which they have speed v2.
For what condition is total internal reflection possible?
v2 > v1
v2 < v1
v2 = v1
All of the above

54. Speed of light in cladding is than speed of light in core.
An Optical Fibre
Speed of light in cladding is than speed of light in core.

55. Medical Fibrescopes
Video-laryngoscopy with a flexible fiberscope

56. Converging Lens , f Focal Point
NOTE: Focal length is defined for initially parallel rays.

57. Diverging Lens Negative , -f Virtual Focal Point
Rays appear to emerge from Virtual Focal Point

58. Diverging rays through a Converging Lens
, f
If an object emits rays at the focal point, they end up being parallel on the other side of the converging lens.

59. They will remain parallel. They will diverge (spread out). f
What will happen to the rays emerging to the right of the lens if the face is moved a little further away from the lens?
They will remain parallel.
They will diverge (spread out).
They will converge (toward a focus).

60. Real Image Formation
, f
image
Light rays actually pass through the image, and a screen can be placed there, so it is “real”.

61. The Camera
A camera “takes a picture” by using a lens to form a real, inverted image on a light-sensitive detector in a light-tight box.
We can model a combination lens as a single lens with an focal length (usually called simply “the focal length”)
A zoom lens changes the effective focal length by varying the spacing between the converging lens and the diverging lens.

62. Wed. June 26 at 1:00pm sharp! (not 1:10!)
This is the end!!!!
The final exam, will be:
Wed. June 26 at 1:00pm sharp! (not 1:10!)
Rooms TBA
Test will begin promptly at 1:00 and will be 2 hours long.
Please bring a calculator, and, if you wish, a letter-sized aid sheet upon which you may write anything you wish

63. This is the end!!!!
The final exam will cover the entire course, including all of the assigned reading plus tutorial materials and what was discussed in class.
Approximately even spread over the course material

64. Final Exam: First Page

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