Upload
jody-flynn
View
215
Download
0
Tags:
Embed Size (px)
Citation preview
DEVIL PHYSICSTHE BADDEST CLASS ON
CAMPUSIB PHYSICS
TSOKOS LESSON A-1THE 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 light-sensitive 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
Color addition – obtaining a color of light by overlapping different amounts of three primary colors
Equal amounts of primary colors yields white light
rRgGbBX
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?
#1-22
Homework