yr9 - refraction, lenses and the eye
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Post on 17-Aug-2015
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- 1. Dr Pusey www.puseyscience.com Q: What are the differences between a convex and concave mirror?
- 2. Recap - Convex & Concave Mirrors Concave Dug out Like a Cave Can form real and virtual images Can focus light Torches & Telescopes Convex Bulges out Makes things appear smaller Security mirrors objects in mirror are closer than they appear www.physicsclassroom.com
- 3. Recap MIRROR Show: Angle of incidence Angle of reflection Normal Reflected Ray Incident Ray
- 4. Recap MIRROR Normal Reflected Ray Incident Ray i r
- 5. Refraction Bending of light Occurs when the light wave enters a different medium and changes speed Light is the fastest in a vacuum (space) Speed (vacuum) = 3x108 m/s When light slows down, it bends TOWARDS the normal
- 6. Why is light refracted? The speed of light depends on the material through which the light is travelling. When light enters a different material (e.g. when moving from air into glass), the speed of light changes. This causes the light to bend or refract. The speed of light is affected by the density of the material through which it is travelling. When light enters a more dense medium, its speed decreases and this is why refraction occurs. air glass
- 7. Your Turn As a wave enters a medium where it travels slower, it bends towards the normal As a wave enters a medium where it travels faster, it bends away from the normal Faster speed Slower speed Normal Normal i r
- 8. Your Turn Glass Show: Angle of incidence Angle of refraction Normal Refracted Ray Incident Ray
- 9. Your Turn Glass Normal i r Incident Ray Refracted Ray What happens when the ray leaves the glass block? Draw it!
- 10. Your Turn Glass Normal Normal i r i r
- 11. Total Internal Reflection If the angle of incidence is large enough, light wont actually refract through to the next medium. It will instead reflect! Diamonds NBN Fibre Optics!
- 12. Lenses Transparent material that direct/refocus light using the principles of refraction Two types for you to learn: Convex Bulges on each side Concave Caves in on each side https://en.wikipedia.org/wiki/Lens_%28optics%29
- 13. Convex Lens Focusses light (e.g. magnifying glass) The point at which light focusses is the focal point https://en.wikipedia.org/wiki/Lens_%28optics%29
- 14. Concave Lens Spreads (diverges) the light The point where the diverging light appears to come from is known as the focal point https://en.wikipedia.org/wiki/Lens_%28optics%29
- 15. Your turn Finish these ray diagrams:
- 16. Your turn Finish these ray diagrams:
- 17. Focuses Light to the Retina to form an image Changes the shape of the lens to focus on near and far objects Contains light receptors. Where images are formed from light Carries signals to the brain Lets light into the eye! Controls how much light is let into the eye Refracts light into the lens for focussing Extension! The Eye
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