phy205 physics of everyday lifejharlow/teaching/every...physics of everyday life class 10: colour,...
TRANSCRIPT
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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
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.
E
M
What property of a light wave mainly
determines its colour?
A. Its frequency
B. Its amplitude
C. Its timbre
D. A mix of all of the above
Why Sunsets Are Red
CHECK YOUR NEIGHBOR
Color we see depends on frequency of light.
High Frequency,
Short
Low Frequency,
Long
𝑓
𝜆
Color
0.4 𝜇m 0.7 𝜇m
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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!
Mixing Colored Light
The spectrum of sunlight is a graph of
brightness versus frequency.
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?
A. It will spread into a small range of
colours.
B. It will change to a single colour other
than green.
C. It will stay green.
Why Sunsets Are Red
CHECK YOUR NEIGHBOR Rods and cones contain stacks of membranes. Rhodopsin is a transmembrane protein complex.
Cone Rod
Light Light
Rhodopsin
Retinal
(pigment)
Opsin
(protein
component)
The retinal molecule inside rhodopsin changes shape when retinal absorbs light.
Light
trans conformation
(activated)
Opsin
cis conformation
(inactive)
0.5 µm
Opsin
Slide courtesy of Ross Koning, Biology Department, Eastern Connecticut State University
http://plantphys.info/sciencematters/vision.ppt
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Slide from http://hyperphysics.phy-astr.gsu.edu/hbase/vision/colcon.html
Response Curves for the three types of cones in
the retina of the human eye.
Use both eyes, stare at area shown in blue for 15 seconds or so
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?
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.
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What colour is
the afterimage
bird?
A. orange
B. green
C. blue
D. yellow
E. None of
the above
Bird Was Red 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.
What colour is
the afterimage
bird?
A. red
B. orange
C. blue
D. violet
E. None of
the above
Bird Was Green 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.
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What colour is
the afterimage
bird?
A. red
B. orange
C. yellow
D. green
E. None of
the above
Bird Was Blue
Additive Primary Colours (light bulbs)
and Subtractive Primary Colours (ink)
Discussion Question
• Why is this square red?
A. The light bulbs in the projector emit light with
blue frequencies
B. The light bulbs in the projector emit light with
green frequencies
C. The light bulbs in the projector emit light with
red frequencies
D. Both A and B
Discussion Question
• Why is the red folder in Harlow’s hand
red?
A. The pigments in the paper absorb light
with blue frequencies
B. The pigments in the paper absorb light
with green frequencies
C. The pigments in the paper absorb light
with red frequencies
D. Both A and B
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• When the colour yellow is seen on the
screen of your computer, what are the
lights being activated in that region of your
screen?
A. Mainly yellow
B. Blue and red
C. Green and yellow
D. Red and green
Discussion Question : Using the
colour wheel..
• If an object is blue, which of the coloured
lights below would make the object appear
most black?
A. blue
B. cyan
C. yellow
D. magenta
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?
A. red
B. orange
C. white
D. cyan
Discussion Question : Using the
colour wheel..
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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.
Why the Sky Is Blue
𝑓𝑟𝑒𝑞𝑢𝑒𝑛𝑐𝑦
If molecules in the sky scattered orange light
instead of blue light, the sky would be
A. orange.
B. yellow.
C. green.
D. blue.
Why Sunsets Are Red
CHECK YOUR NEIGHBOUR 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.
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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”
Why Sunsets Are Red
Light that is least scattered is light of low
frequencies, which best travel straight through air.
If molecules in the sky scattered orange light
instead of blue light, sunsets would be
A. orange.
B. yellow.
C. green.
D. blue.
Why Sunsets Are Red
CHECK YOUR NEIGHBOUR
Why Clouds Are White
• Clouds are clusters of various sizes of water droplets
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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.
What does a white sky indicate?
A. The atmosphere has mostly particles smaller
than the wavelength of light
B. The atmosphere has mostly particles larger
than the wavelength of light
C. The atmosphere has a mixture of particle sizes
D. The atmosphere has a lot of water vapour
E. The atmosphere is filled with pollutants.
Why Sunsets Are Red
CHECK YOUR NEIGHBOR
Law of Reflection The angle of reflection equals the angle of incidence.
© 2010 Pearson Education, Inc.
Mirror
• 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?
A. 90°
B. 45°
C. 180°
A
B
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Virtual Image Formation
No light rays actually pass through or even near the image, so it is “virtual”.
Two plane mirrors form a right angle.
How many images of the ball can the
observer see in the mirrors?
A. 1
B. 2
C. 3
D. 4
• Which picture is most likely a mirror image of
Harlow? • 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.
Virtual Image Formation
• 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?
mirror real
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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?
Virtual Image Formation • What really happens is the image is reversed
front-to-back
Refraction
When light bends in going obliquely from
one medium to another, we call this process
refraction.
Cause of Refraction • Bending of light when it passes from one medium
to another
• Caused by change in of light
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Dry Land
Mud
Dry Land
1
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?
A B C
Refraction
Light travels in glass than in air, so it
minimizes the time it spends in the glass.
© 2010 Pearson Education, Inc.
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.
air
water
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).
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Rainbows
Rainbows are a result of dispersion by many drops.
• Dispersion of light by a single drop
Rainbows
Antisun
Radius of circle is about 41°
Double-
rainbow
The second rainbow
has blue on the top,
and a radius of about
53°
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
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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?
A. v2 > v1
B. v2 < v1
C. v2 = v1
D. All of the above
An Optical Fibre
Speed of light in cladding is than
speed of light in core.
Medical Fibrescopes
Video-
laryngoscopy
with a flexible
fiberscope
Converging Lens
Focal Point
, f
NOTE: Focal length is defined
for initially parallel rays.
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Diverging Lens
Virtual Focal
Point
Negative
, -f
Rays appear to emerge
from Virtual Focal Point
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.
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?
A. They will remain parallel.
B. They will diverge (spread out).
C.They will converge (toward a focus).
f Real Image Formation
, f
Light rays actually pass through the image, and a screen can be placed there, so it is “real”.
image
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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.
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
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
Final Exam: First Page
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