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SCIENCE 8 Ms. Rodriguez UNIT 4: Chapter 5 – Human Eye CHAPTER 5 – Human Eye 6.1 Human Vision How Light Enters the Eye • ____________ – opening that appears dark because light passes through it without reflecting back. • ____________ – coloured circle of muscle surrounding the pupil. It controls the amount of light entering the eye. o Dilates (expands) Æ when it is ____________ (see p. 203) o Contracts (closes) Æ when it is ____________ • ____________ – cells that are transparent enough to let light pass through, yet tough enough to hold the eye together. • ____________ – white tissue surrounding the iris. Light passes through the pupil and through a ____________ lens. This light ____________ and focuses (with the help of the lens) on a screen at the back of the eye called the ____________. • ____________ – the back of the eye where images are formed. It contains special light‐
sensitive cells that detect the image. Other cells convert the light rays into electrical signals which are then sent to the brain. • ____________ ____________ – transmits the electrical signals to the brain. The eye is filled with a watery fluid that ____________ the cornea/lens, gives ____________ to the eye, and also provides ____________ to the cornea (does not have any blood vessels). The lens has the ability to fine‐tune focussing by changing its ____________. • When muscles in the eye contract Æ ____________ tension on the lens Æ lens becomes ____________ Æ focus on ____________ objects. • When muscles in the eye relax Æ ____________ tension on the lens Æ lens becomes ____________ Æ focus on ____________ ____________ objects. The images formed on the back of your retina are ________________________. However, your brain will interpret these images and so you will see them as upright. Blind Spot (see figure 6.5 on page 205) • The area where the optic nerve enters the retina has no ________________________. • Each eye sees what the other eye misses because blind spots are not in the same place for each eye. Black‐and‐White Vision and Colour Vision 1. Rod cells – help determine ____________, ____________, and shades of ____________ 2. Cone cells – three different kinds which help detect ____________. If equal amounts of red, green and blue are seen Æ we see ____________. SCIENCE 8 UNIT 4: Chapter 5 – Human Eye Correcting Focus Problems Vision Description Diagram Normal Light rays will go through the ____________ lens, causing them to ____________ and focus. The eye will adjust (change shape) to focus light into a clear image. Near‐sighted The inability to see ____________ objects. Lens converges light ____________ (in front of the retina) so by the time it reaches it, the rays spread out again (causing a fuzzy image). Use a ____________ lens to diverge the rays farther back on the retina. Far‐sighted The inability to see objects ____________ . Lens converges light ____________ (behind the retina) so the image is fuzzy (not focussed). Use a ____________ lens to converge the rays closer on the retina. Astigmatism Ms. Rodriguez ____________ ____________ cornea causes an image (see figure 5.10, p.209) to focus on more than one point on the retina. Glasses, contacts or laser surgery are used to correct the problem. Blindness Any form of vision impairment: • ____________ blindness – painful condition of temporary partial or complete blindness caused by overexposure to the glare of sunlight. Treatment: resting eyes in a dark room for days. • ____________ blindness – difficulty or impairment to see in dim light. Cause: rod cells losing ability to respond to light due to injury or malnutrition. • ____________ blindness – ability to see only shades of grey. Occurs in 1/40000 people. • Colour ____________ ____________ – inability to distinguish certain colours. Occurs in 8% of males, 1% of females. Most common type is the inability to distinguish red from green. 6.2 Extending Human Vision • Microscopes: use two ____________ lenses with ____________ focal lengths to magnify small, close objects. o Because the microscope has two lenses, the image is magnified ____________, resulting in a final image that can be hundreds of times larger than the actual object. SCIENCE 8 Ms. Rodriguez UNIT 4: Chapter 5 – Human Eye • Telescopes: use a ____________ or ____________ mirror that is much larger than your eye to gather more light from distant objects. As a result, images appear to be much ____________ and therefore can be magnified to a greater extent, revealing more detail. o Have ____________ focal lengths than lenses in a microscope in order to view objects far away. o ____________ telescopes – bend light to focus it. ƒ Problems: large lenses are heavy and therefore can sag or flex. This causes distortions in the images they produce. o ____________ telescopes – use a concave mirror, plane mirror, and convex lens to collect and focus light. ƒ Light enters and hits a concave mirror at one end converging the light, then strikes a plane mirror placed at an angle which bounces the light towards the eyepiece (convex lens). •
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Binoculars: two ____________ telescopes mounted side by side. o ____________ are placed inside to serve as plane mirrors (which would be used in telescopes). The prisms ____________ the light back and forth in a shorter tube. Cameras: gathers and bends light with a ____________ lens. The lens projects an image onto a light detector to record a digital image. The image formed is ____________ and ____________. o ____________ – the opening where light enters the camera. o Wide‐angle lens – have ____________ focal lengths that produce a relatively ____________ image but have a wide field of view. o Telephoto lens ‐ have ____________ focal lengths that produce an image that seems ____________ and closer than it actually is. SCIENCE 8 Ms. Rodriguez UNIT 4: Chapter 5 – Human Eye Cameras and the Human Eye Similarities Differences • ____________ ____________ of a camera • To focus a camera, change the ____________ between the lens and the and the human ____________ both protect the lens from damage. detector. In humans, the lens changes ____________ to focus. • The ____________ (series of opaque circles) of a camera and the ____________ both limit the amount of light entering the eye. • ____________ (charge‐coupled device) of a camera absorbs light and provides electrical signals to produce an image. ____________ record a tiny part of the image. These correspond to the rods and cones in our eyes that detect light. • Lasers: contain light that has the same ____________, and all move in the same ____________ with crests and troughs lined up. o Travel great distances without spreading out and contain high levels of ____________. o Does not refract into a rainbow because it contains only ____________ wavelength. o Uses: ƒ ____________ ____________ – cataracts are when the lens becomes cloudy and must be replaced with synthetic ones. ƒ ____________ ____________ – used to weld the retina back in place and prevent further detachment. ƒ ____________ ____________ – seals off blood vessels and is used during surgery to reduce bleeding. ƒ ____________ ____________ – lasers are used to weaken the outer layer so it can be folded back. The inner layers are then reshaped, and the outer layers are folded back. • Optical fibres: ____________ glass fibres that can transmit light from one place to another. o Total internal reflection – light entering one end of the fibre is reflected from side to side until it emerges from the other end. o Uses: ƒ used in ____________ to transmit images of the inside someone’s body from a tiny camera at the end of an optical fibre to a monitor. ƒ Used in ____________ to transmit phone, video and internet signals all done the same cable without interfering with one another (because of their different wavelengths).