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# Light, Lenses & the Human Eye

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• Review Question: If radio signals are really made up of light, why doesn&apos;t a radio station&apos;s antenna glow when it transmits its signals? A radio station&apos;s antenna does not glow because the light it emits is not visible . Radio waves have wavelengths longer than visible light.
• Light waves slow down in a denser or more solid medium and speed up with less matter (less dense or less solid). Sound waves speed up in a denser or more solid medium and slow down the less matter there is (less dense or less solid).
• At roughly age 50, the lens can no longer change shape and becomes more yellow with age: Cataracts
• ### Light, Lenses & the Human Eye

1. 1. Light, Lenses & The Human Eye Powerpoint Templates
2. 2. Wave Reflection• A reflection occurs when a wave hits a surface and bounces off – All types of waves can be reflected – angle of incidence = angle of reflection Powerpoint Templates
3. 3. Refraction• As waves travel from one medium to another, some waves are reflected (bounce back) and others are refracted ("bent" into a new direction)• Examples: – air to glass to air • Store window – air to glass to water • pencil in water cup – layers of Earth • seismic waves – air to water • The Gar Story Powerpoint Templates
4. 4. Direction of Refraction Fast Medium reflected light normal• If waves slow down the direction will bend towards the normal – The normal is a line that is perpendicular to the surface that it strikes. – Example: light traveling through space, then air, then water• If waves speed up, the direction will bend away from the normal – Examples: • sound traveling through air, then water • light traveling through glass, thenTemplates Powerpoint air
5. 5. Refraction in a Curved Surface• A light ray will bend towards the perpendicular normal when it slows down as it passes through this glass lens.• As the light ray exits the lens, it will bend away from the perpendicular normal because it speeds up as enters the air.• The normal is different at each point because the surfaces are curved. Powerpoint Templates
6. 6. • If you were to do this for several light rays that travel horizontally towards the object, you would get the following picture:• The single point through which all rays pass (where they meet or converge) is called the focal point. – The thicker a lens is, the more refraction occurs: Powerpoint Templates
7. 7. Convergent & Divergent Lenses• Convex lenses refract light in a towards each other: convergent• Concave lenses refract parallel light rays away from each other: divergentLight that travels through the center of either lens continues straightthrough and is NOT refracted. Powerpoint Templates
8. 8. Convex Lens• Refraction Rules for a Converging Lens: – A ray traveling parallel to the axis of a converging lens will refract through the lens and travel through the focal point on the opposite side of the lens. – A ray traveling through the focal point on the way to the lens will refract through the lens and travel parallel to the axis. Powerpoint Templates
9. 9. Concave Lens• Refraction Rules for a Diverging Lens – A ray traveling parallel to the axis of a diverging lens will refract through the lens and travel in line with the focal point. – A ray traveling towards the focal point on the way to the lens will refract through the lens and end up parallel to the axis. • In this case, the focal point is negative or virtual (the rays never actually pass through the focal point. Powerpoint Templates
10. 10. Reflection and Sight• How does this woman see her foot in the mirror? – Light reflects off of her foot, hits the mirror, reflects off the mirror, and enters her eyes• Her brain assumes light travels in a straight line. – The brain interprets the image as being inside the mirror. Powerpoint Templates
11. 11. The Human Eye Powerpoint Templates
12. 12. The Human Eye• Sclera – White, tough sheath around the eye. – Tendons attached to it for movement.• Cornea – Clear bulging surface in front of the eye. – Refracts light to help focus images.• Iris – Colored muscle near center of the eye. – Adjusts diameter of pupil to control how much light enters.• Lens – Transparent body enclosed in a capsule. – Attached muscles (ciliary body) adjust thickness of lens to change amount of refraction and focus images.• Retina – Lining in the back of the eye containing millions of light-sensing cells that transform light waves into electric nerve impulses.• Optic Nerve – Carries light information to theTemplates interpretation. Powerpoint brain for
13. 13. The Human Eye• What type of lens does your eye have? Double Convex• How Vision Works video Powerpoint Templates
14. 14. Corrective Lenses• Normal vision: – image is focused on the back of the retina• Myopia (nearsightedness) – eyeball is too long, so image is focused in front of retina – concave lens corrects vision• Hyperopia (farsightedness) – eyeball is too short, so image is focused behind retina – convex lens corrects vision Powerpoint Templates