SCIENCE 8 WORKBOOK Chapter 6 Human Vision Ms. Jamieson 2018 This workbook belongs to: Eric Hamber Secondary 5025 Willow Street Vancouver, BC
Table of Contents A. Chapter 6.1 Parts of the eye.. Parts of the eye functions.. The path of light. Why are images upside down on the retina?. Ray diagrams practice How can lenses help correct vision problems? Lenses and light rays review. Correcting vision problems Inside the eye.. Powerpoint notes- how do we see colour? Rods and cones.. Parts of the eye crossword puzzle 1 2 3 4 5 6 7 8 9 10 11 13 Science 8 Workbook Ms. Jamieson 2018
What s inside your eyeball? Read pages 202-205 in your textbook. Label the parts of the eye in the diagram below. Then fill in the chart of the functions of each part of the eye. * means the part is not described in the BC Science 8 text. We will go over these parts in class 1) 8) 5) Science 8 Workbook Ms. Jamieson 2018 1
What do the parts of the eye do? # NAME OF THE PART WHAT IT DOES 1 2 3 4 5 6 7 8 9 10 11 12 13 Sclera Choroid Retina Fovea (aka focal point) Iris Blind spot Lens Pupil Cornea Aqueous humour Vitreous humour Optic nerve Ciliary muscle/body opaque tissue tough outer layer of the eye protects the eyeball contains blood vessels that nourish the retina layer of light sensing cells area of retina where light sensing cells are most numerous coloured ring of muscle controls the size of the pupil where optic nerve enters retina there are no light-sensing cells flexible transparent convex structure helps focus light opening in the centre of the eye where light enters transparent part of sclera does most of the focusing of light rays holds cornea away from iris/pupil and nourishes cornea jelly like fluid helps the eye keep its shape, keeps retina in place connects the eye to the brain, transmits signals to brain holds lens in place and changes shape of lens to focus Science 8 Workbook Ms. Jamieson 2018 2
The Path of Light List the parts of the eye that light rays pass through from outside the eye to the retina Cornea Aqueous humour Pupil Lens Vitrous Humour Retina Show how the image of the tree appears on the retina and then in the brain Science 8 Workbook Ms. Jamieson 2018 3
Why are images upside down on the retina? Images are upside down on the retina because of the way convex lenses refract light rays. We can use a ray diagram to show how a lens refracts light rays and creates an image. Use the following instructions to complete the ray diagram of light rays passing through a lens and forming an image on the retina. 1. Light rays reflect off objects in all directions. In this ray diagram we will look at only three light rays, all reflecting from the tip of the arrow. 2. First, label the principal axis, the vertical axis, the focal points and the 2F points on the diagram. 3. These are the rules for how light rays refract through convex lenses: Any incident light ray traveling toward the lens parallel to the principal axis will refract at the vertical axis and then travel through the focal point on the opposite side of the lens. Use a ruler to draw one light ray coming from the tip of the arrow that follows this rule Any incident ray traveling through the focal point on the way to the lens will refract at the vertical axis of the lens and then travel parallel to the principal axis on the other side of the lens. Use a ruler to draw a second light ray from the tip of the arrow that follows this rule Any incident ray that passes through the center of the lens (where the principal axis and vertical axis meet) will continue to travel in the same direction on the other side of the lens. Use a ruler to draw a third light ray from the tip of the arrow that follows this rule The point where the refracted light rays intersect is where the image of the tip of the arrow will form on the retina. Draw the image of the arrow. The base of the image will be on the principal axis and the tip will be where the refracted light rays intersect 4. Is the image upright or upside down?. Is the image larger or smaller than the object?. How far is the object from the lens? 5. Compare the ray diagram you drew with what you already know about how convex lenses form images. Does it make sense? Science 8 Workbook Ms. Jamieson 2018 4
Ray diagrams practice 6. Now draw and label ray diagrams for the images below. Each object is at a different distance from the lens. Label the vertical axis, principal axis, focal points and 2F points. Draw the incident and refracted rays and the image according to the rules on page 4. a) The object is between 1 and 2 focal lengths from the lens: Is the image upright or upside down? Is the image larger or smaller than the object (the arrow)? b) The object is less than 1 focal length from the lens: NOTE: You will need to trace dotted virtual light rays backward from the refracted rays. The point where the virtual rays intersect is the tip of the virtual image of the arrow. Is the image upright or upside down? Is the image larger or smaller than the object (the arrow)? c) The object is at the focal point. NOTE: This will produce no image. Draw the rays to show why. Why do you think no image is produced when the object is at the focal point? 7. Compare the ray diagrams you drew with what you already know about how convex lenses form images. Do these diagrams make sense? Science 8 Workbook Ms. Jamieson 2018 5
How can lenses help correct vision problems? 6.1 Human Vision Nearsightedness Farsightedness Astigmatism Science 8 Workbook Ms. Jamieson 2018 6
Lenses and light rays review 1. How do lenses refract light rays? a) How do convex and concave lenses refract light rays? b) How do parallel and diverging incident rays affect where the focal point is in a convex lens? c) How does the thickness of a convex lens affect where the focal point is in a convex lens? 2. Which lens refracts (bends) light more, a thick convex lens or a thin convex lens? Thick convex lens 3. List 3 ways that the focal point in the eye can be brought closer (hint: one way involves corrective lenses) 1. Farther away from the object (parallel rays) 2. Thicker lens inside the eye 3. Convex corrective lens in front of eye 4. List 3 ways that the focal point in the eye can be made farther away (hint: one way involves corrective lenses) 1) Closer to the object (diverging rays) 2) Thinner lens inside the eye 3) Concave corrective lens in front of eye Science 8 Workbook Ms. Jamieson 2018 7
Correcting Vision Problems Fill in the chart below with diagrams. Each diagram should show the shape of the eyeball, the shape of the lens, the incident rays, the refracted rays, the focal point, and the corrective lens (if used) Shape of Eyeball Viewing Distant Object Viewing Close Object Normal Eyeball See the summary in the class notebook for January 10th Long Eyeball (Near-sighted or Myopic vision) Long Eyeball with Corrective Lens Short Eyeball (Far-sighted vision) Short Eyeball with Corrective Lens Science 8 Workbook Ms. Jamieson 2018 8
Cornea Converge Low Convex Upside down Electrical signals Far-sighted Convex Science 8 Workbook Ms. Jamieson 2018 9
See the Powerpoint in the class notebook January 10th 6.1 Human Vision Powerpoint notes - How do we see colour? 1) How does your eye detect colour? The retina is made up of 2 kinds of Light A. around the of the retina. sensitive to. B. in the of the retina (the fovea). sensitive to different of light. Humans have 3 kinds of cones: Red cones - sensitive to wavelengths Green cones - sensitive to wavelengths Blue cones = sensitive to wavelengths Nerve cells Nerve cells 2) How does your brain know what colours you are seeing? The colour you see is a result of the way your brain interprets the combination of the of light detected by the cones the of light detected by the rods results when one of the 3 types of cones is absent or not functioning. 3) Why do we have a blind spot? Colour the spectrum above What colour are red cones most sensitive to? Why are they called red cones? Science 8 Workbook Ms. Jamieson 2018 10
Rods and Cones Part 1 Use the table at right to answer questions 1-2. Note: pigment is the chemical that detects light in light-sensitive cells 1) Why are rod cells more useful for night vision? More light sensitive More of them 2) Why are cone cells more useful for colour vision? Sensitive to different light wavelengths 3) Why is it necessary to have three kinds of cone cells operating in order to have full colour vision? With three kinds of cones you can tel the difference between different wavelengths. If you only had one or two types, the colours would all start to look the same 4) Most mammals, including dogs and cats, cannot see colours. How would the retina of a cat s eye be different from the retina of a human eye? Dogs and cats CAN actually see colours, but not the number of different colours that humans can. A cat retina would only have two types of cones blue and red/green 5) Place the letters of the following descriptions into the appropriate circle: 100 million 1 type Evenly distributed Lots of pigment Used in low light Night vision Slow response to light 6 million 3 types Mostly in centre of retina Very little pigment Used in bright light Day vision Fast response to light Science 8 Workbook Ms. Jamieson 2018 11
Part 2 Use the graph below to answer questions 6-8 B BW G R Colour the spectrum at left About 625 nm yellow red They are the only ones that detect red 525 nm green Because the rods are most sensitive to green light and rods are more light-sensitive than cones and there are more of them Science 8 Workbook Ms. Jamieson 2018 12
Parts of the Eye Crossword Puzzle Science 8 Workbook Ms. Jamieson 2018 13