DEVIL PHYSICS
THE BADDEST CLASS ON CAMPUS
IB PHYSICS
TSOKOS LESSON A-1
THE EYE AND SIGHT
Reading Activity Questions?
IB Assessment Statements
SL Option A-1, The Eye and Sight:
A.1.1. Describe the basic structure of the
human eye.
A.1.2. State and explain the process of depth of
vision and accommodation.
A.1.3. State that the retina contains rods and
cones, and describe the variation in
density across the surface of the retina.
IB Assessment Statements
SL Option A-1, The Eye and Sight:
A.1.4. Describe the function of the rods and
cones in photopic and scotopic vision.
A.1.5. Describe colour mixing of light by
addition and subtraction.
A.1.6. Discuss the effect of light and dark, and
colour, on the perception of objects.
Objectives
 Make an annotated diagram of the eye
 Explain the function of the main parts of
the eye
 Outline the differences in the density of
rods and cones across the retina
 Define scotopic vision and photopic
vision
Objectives
 Account for the differences in scotopic
and photopic vision
 Understand the terms primary colour
and secondary colour
 Understand the differences between
addition and subtraction of colours
Objectives
 Solve simple problems with colour
mixing
 Understand the role of light in the
perception of colours
Video – Light and Images
Video – The Eye
Parts of the Eye
Parts of the Eye
 cornea – transparent
membrane where
most of the
refraction takes
place. Refractive
index is 1.37
Parts of the Eye
 aqueous humour –
liquid-filled chamber
between cornea and
eye lens, index of
refraction index of
1.33, almost same as
water
STOPPED HERE
ON 5/13/13
Parts of the Eye
 iris – colored part
of the eye
Parts of the Eye
 pupil – aperture
through which light
enters the eye; can
increase or
decrease diameter
to adjust to varying
intensities of light
Parts of the Eye
 lens – curvature
can change to
focus objects
 ciliary muscles –
control the
curvature of the
lens when focusing
Parts of the Eye
 vitreous humour –
jelly-like substance
in the inner
chamber of the eye
Parts of the Eye
 retina – back
surface of the eye;
covered with lightsensitive rods and
cones that record
the arrival of light
Parts of the Eye
 rods and cones –
light reaching
these cells is
converted to tiny
electrical signals in
the nerve fibers
attached to them
Parts of the Eye
 optic nerve –
transmits the
electrical signals
from the rods and
cones to the brain
Parts of the Eye
 fovea – a spot of
about 0.25mm
diameter where
vision is acute;
filled with cones
Density of Rods and Cones
 Not constant
 At the fovea, many cones, but no rods
 Density of cones reaches 150,000 per mm2 at
the center
 Rods mainly at the edges of the retina
 Concentration of cones increases as we
approach the principal axis
Functions of the Eye
Depth of Vision
 As light passes
through the
eye lens (or any
converging lens
for that
matter), the
light is
refracted to a
focal point
Depth of Vision
 The eye cannot
focus on
objects at
different
distances at
the same time
 However, they can focus sufficiently to
make things out and the brain helps to fill
in the gaps
Depth of Vision
 Depth of vision is the range of distances
from the eye within which objects can be
seen acceptably clearly
Depth of Vision
 Depth of vision depends on distance and
lighting
 The further the object is away, the larger the depth
of vision
 The brighter the lighting, the larger the depth of
vision
Accommodation
 Does not refer to a place to stay while on
vacation
 Ability of the eye lens to change the focal
length by contracting the ciliary muscle
Accommodation
 When the ciliary
muscle is relaxed,
the connective tissue
to the lens is taut
causing it to stretch
the lens so it is flat
and can focus on
distant objects
Accommodation
 When the ciliary
muscle is
contracted, the
connective tissue to
the lens is relaxed
allowing the lens to
bulge (its natural
state) and the eye
can focus on near
objects
Accommodation
 ‘Eye strain’ occurs
when the ciliary
muscles are
contracted for long
periods of time
 When working with
close-in objects, you
should take breaks to
focus on distant
objects
Near Point and Far Point
 The near point, or closest point the eye
can focus on without undue strain, is
about 25cm in most people
 The far point, or furthest point a person
can focus on clearly, for most people is at
infinity
Scotopic and Photopic Vision
 Scotopic vision – vision in which the main
detectors of light in the eye are the rods
 Rods are better at vision in low levels of light
intensity, but not at detecting detail in an
object
 Rods do not distinguish colors
Scotopic and Photopic Vision
 Photopic vision – vision in which the
cones are the main detectors of incident
light
 Cones are only receptive in high intensity light
 Better at detecting detail
 Do distinguish between colors
Scotopic and Photopic Vision
 Why does the
night sky appear
black and white,
whereas
telescopic
pictures of
distant galaxies
show lots of
color?
Scotopic and Photopic Vision
 The ambient light
is low and the
light coming from
stars is relatively
low so scotopic
vision is in use
and colors aren’t
distinguished.
Scotopic and Photopic Vision
Scotopic and Photopic Vision
Colour
 Three types of cone
cells sensitive to
either blue, green,
or red light
 Different mixtures
of these will
produce the
spectrum of colors
Colour
 For example, wavelengths between 550nm
and 650nm only excite green and red cones
giving varying shades of yellow
Color Blindness
 Affects men more than women
 Complete color blindness is rare
 Most common is inability to distinguish
between red and green (why you look
both ways before crossing an
intersection, even on a green light)
Color Blindness
 Caused by either defective cones of a
certain color, or a deficiency of a specific
color cone
 Could be caused by brain damage or
damage to the optic nerve
 Prevents you from getting a pilot license
 How come?
Color Blindness Test
 http://www.biyee.net/color-science/color-
vision-test/
Color Blindness Test
Colour Addition
 Combination of the primary colors red,
green and blue gives any color
X  bB  gG  rR
 Color addition – obtaining a color of light by
overlapping different amounts of three
primary colors
 Equal amounts of primary colors yields
white light
Colour Addition
 Adding primary colors two at a time yields
secondary colors cyan, magenta, and
yellow
 B + G = C (Cyan)
 B + R = M (Magenta)
 R + G = Y (Yellow)
 Other primaries can be used, but RGB is
most common
Colour Addition
 If the third primary is added to a secondary,
you get white light
 C + R =W
 M +G =W
 Y + B =W
 The primary color added to the secondary
color to give white light is called the
complementary colour of the secondary
Colour Addition
 Adding primary colors two at a time yields
secondary colors cyan, magenta, and yellow
 B + G = C (Cyan)
 B + R = M (Magenta)
 R + G = Y (Yellow)
 Secondary colors are also called primary
pigments. While it is hard to know exactly what
the pig meant, it is an economical way to
manufacture printer ink. Why do printers use
the secondary colors instead of primary colors?
Colour Subtraction
 When white light is transmitted through a
coloured filter; the transmitted light has
the color of the filter because the filter
removes that color from the white light.
 Secondary colors are primarily used for
filters
Colour Problems
 What color of light is obtained when we
overlap equal intensities of magenta with
yellow?
Colour Problem
 What color of light is obtained when we
overlap equal intensities of magenta with
yellow?






Magenta = R+B
Yellow = R+G
M+Y = R+B+R+G
M+Y = (R+G+B)+R
M+Y = W+R
M+Y = Red
Perceptions From Color and Light
 Light has been found to have a
psychological effect
 Red and yellow give the sense of busy or
hurried
 Pastel colors give the sense of calm,
peace
 Soft reddish orange create a warm
atmosphere
Perceptions From Color and Light
 Blue or violet give the impression of
coolness or cold
 Light colors make a room appear larger,
dark makes them seem smaller
 Dark shadows give the appearance of
mass, light shadows give the appearance
of lightness or airyness
Σary Review
 Can you make an annotated diagram of
the eye?
 Can you explain the function of the main
parts of the eye?
 Can you outline the differences in the
density of rods and cones across the
retina?
 Can you define scotopic vision and
photopic vision?
Σary Review
 Can you account for the differences in
scotopic and photopic vision?
 Do you understand the terms primary
colour and secondary colour?
 Do you understand the differences
between addition and subtraction of
colours?
Σary Review
 Can you solve simple problems with
colour mixing?
 Do you understand the role of light in
the perception of colours?
IB Assessment Statements
SL Option A-1, The Eye and Sight:
A.1.1. Describe the basic structure of the
human eye.
A.1.2. State and explain the process of depth of
vision and accommadation.
A.1.3. State that the retina contains rods and
cones, and describe the variation in
density across the surface of the retina.
IB Assessment Statements
SL Option A-1, The Eye and Sight:
A.1.4. Describe the function of the rods and
cones in photopic and scotopic vision.
A.1.5. Describe colour mixing of light by
addition and subtraction.
A.1.6. Discuss the effect of light and dark, and
colour, on the perception of objects.
QUESTIONS?
Homework
#1-22