Pirate Vision
On your way in, please pick up:
• Eye Patch (just one - there are two kinds)
•
(we’ll wear these later in the class)
Pulfrich Glasses (one dark, one light lens)
1
Week 16: Exam #3
Exam time:
Monday, May 12
8:00 - 9:30 AM
Exam location:
• Surnames Q-Z:!
• Surnames A-C:!!
• Surnames H-L:!!
• Surnames D-G:!
• Surnames M-P:!!
Clark A201
Clark A202
Clark A203
Clark A204
Clark A205
Details:
• Cumulative. 5 scenarios, pick 4.
• You may bring three study sheets and right hand rule devices.
Post-Exam Reception:
Thursday, May 15
6:00 - 10:00 PM
Brian & Carol’s
2
Week 15: Review
Monday: Pirate Vision
• course overview
• review and applications, with a focus on optics
Tuesday: Recitation
• exam practice
All Week: Lab
• Little Shop of Physics
Wednesday: Spot the Physics!
• analyzing physical situations and problems
Friday: Review and Closure
• exam scenario practice
3
Power of
visual
system
1
1
= 60 +
f
s
Power (D)
60
61
62
63
64
65
70
Distance (m)
∞
1.0
0.50
0.33
0.25
0.20
0.10
Viewing
distance
A myopic man
has a far point
of 50 cm.
What power
lens does he
need?
4
With my -5.0 D corrective lenses, my distant
vision is quite sharp; my near point is 1.0 m.
I have a pair of -3.5 D computer glasses that put
my computer screen right at my near point.
• How far away is my computer?
• What is my far point with these glasses on?
5
Electricity, Magnetism: 5 Key Concepts
• Charge & charges in matter
• The field model
‣Electric field exerts force on charges, magnetic field exerts force on
moving charges.
‣Electric field due to charge distribution, magnetic field due to
currents.
• Potential & circuits
‣Basic circuit, resistance
‣More complex circuits
• Changing magnetic field induces emf
• Electromagnetic waves
‣Nature of waves
‣Spectrum of waves
6
Modern Physics: 3 Key Concepts
• Quantum notions
‣Particle nature of light
‣Wave nature of matter
• Quantum consequences
‣Discrete energy levels & transitions
• Nuclear physics:
‣Decay
‣Radiation
7
Optics: 3 Key Concepts
• Wave properties:
‣Interference
‣Diffraction
• Reflection & refraction
• Optics:
‣Lenses & images
‣Vision and vision correction
8
9
The Eye
10
In water, are you nearsighted or farsighted?
11
Underwater vision correction?
Air lens in water.
Converging or diverging?
12
Horse Sense
The ciliary muscles in a horse’s eye can only make small changes to the shape
of the lens, so a horse can’t change the shape of the lens to focus on objects at
different distances as humans do. Instead, a horse relies on the fact that its
eyes aren’t spherical. As the figure shows, different points at the back of the
eye are at somewhat different distances from the front of the eye.
We say that the eye has a
“ramped retina”; images that
form on the top of the retina are
at a greater distance from the
cornea and lens than those that
form at lower positions. The
horse uses this ramped retina to
focus on objects at different
distances, tipping its head so that
light from an object forms an
image at a vertical location on
the retina that is at the correct
distance for sharp focus.
Lens
Iris
Cornea
m
45 m
43 mm
Retina
40 m
m
13
In a horse’s eye, the image of a close object will be in focus
! A.!! At the top of the retina.
! B.!! At the bottom of the retina.
In a horse’s eye, the image of a distant object will be in focus
! A.!! At the top of the retina.
! B.!! At the bottom of the retina.
Lens
Iris
Cornea
m
45 m
43 mm
Retina
40 m
m
14
A horse is looking straight ahead at a person who is standing quite
close. The image of the person spans much of the vertical extent of
the retina. What can we say about the image on the retina?
!
!
!
!
A.! The person’s head is in focus; the feet are out of focus.
B.! The person’s feet are in focus; the head is out of focus.
C.!The person’s head and feet are both in focus.
D.! The person’s head and feet are both out of focus.
Lens
Iris
Cornea
m
45 m
43 mm
Retina
40 m
m
15
Certain medical conditions can change the shape of a horse’s eyeball;
these changes can affect vision. If the lens and cornea are not changed
but all of the distances in the figure are increased slightly, this will
make the horse
!
!
!
A.! Nearsighted.
B.! Farsighted.
C.!Unable to focus clearly at any distance.
Lens
Iris
Cornea
m
45 m
43 mm
Retina
40 m
m
16
The Vision Thing
The cornea and lens of your eye work together as a single-lens system that focuses an image on your retina. Most of
the focusing power comes from the refraction when light hits your cornea. To focus on objects at different distances,
muscles in your eye work to change the shape—and thus the power—of the lens. If the range of power of your visual
system isn’t matched to the length of your eyeball, you may suffer from myopia or hyperopia—nearsightedness or
farsightedness.
When you open your eyes underwater, the change in refraction at the cornea leads to blurry vision. Animals that can
see well above and below the water have adaptations that allow them to correct for this effect. For instance, penguins
are capable of a very high degree of accommodation that allows them to see well both above and below the water.
Multiple Choice Questions
1) A nearsighted person has a far point of 40 cm. What power corrective lens is required for comfortable distance
vision?
A. 4.0 D
B. 2.5 D
C. –2.5 D
D. –4.0 D
2) Everyone’s vision is compromised underwater, but some can see better than others. Who would have the clearest
vision underwater?
A. A person with vision that requires no correction.
C. A person with hyperopia.
B. A person with myopia.
D. A person with presbyopia.
Short Answer Question
The rod and cone cells in the central part of the retina—the fovea—are packed more closely, giving a more detailed
view. This area of increased rod and cone density has a diameter of about 1.5 mm. When you read a book, you want
the image of the text you are reading to fall on the fovea. If you hold a book 30 cm from your eyes, how wide is the
spot on the page whose image just fills the fovea? That is, how wide an area do you see most clearly? Assume that the
image on the retina forms 17 mm from the lens in the eye (which gives 1/s’=60.)
17
Recall the Primary and Complementary Colors:
Primary Colors
Red
Green
Blue
Complementary Colors
Cyan
Not Red
Magenta Yellow
Not Green Not Blue
18
Retinal linked to the
rhodopsin in rod cells
(responsible for vision in
dim light) has a threshold
photon energy of 1.8 eV.
Explain why astronomers
use red flashlights.
19