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 ImagesLight and Images

Video – The EyeThe 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

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 mm 2 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

ColourColour  Three types of cone cells sensitive to either blue, green, or red light  Different mixtures of these will produce the spectrum of colors

ColourColour  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  vision-test/ 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

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.

#1-22 Homework