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Transcript

  • 1. 11.3 Limitations of our eyes
  • 2. - We can see many things, but we cannot see things at all distances or of all sizes . - For people with normal eyesight, they still have limitations of their eyes.
  • 3. 1 object is too near p.76 Limitations of our eyes 2 object is too far away 3 object is too small cannot see / cannot see clearly
  • 4. We can overcome some of the limitations by using suitable instruments.
  • 5. p.77 Extending our vision Separate the following instruments into two groups according to their functions and arrange them in the order of how well they serve that function. Activity Corner C
  • 6. A B C D E F Microscope Telescope Binoculars Electron microscope Hand lens Distant objects Small objects 1 Astronomical telescope 3 2 1 2 3 Video Video
  • 7. We cannot see clearly when the object is too small, too near or too far away. There is another limitation of our eyes  blind spot. What is blind spot? Find it out from Activity Corner E
  • 8. p.80 Why does the ghost disappear? 1 Hold your book at your eye level. Cover your left eye. Look at the cross at the top of the castle in the picture below. Can you see the ghost and the cross at the same time? ___ Activity Corner E
  • 9. 2 Repeat step 1. This time, keep looking at the cross while you slowly move the book towards you . Can you see the ghost all the way through? blind spot We cannot see the object when its image falls on the ___________ of the retina.
  • 10. Is there also a blind spot in your left eye? _______ 3 Repeat the experiment. This time, cover your right eye. Can you see the ghost all the way through?
  • 11. p.81 blind spot ( 盲點 ) - Where the optic nerve leaves the eye - There are no light-sensitive cells => We are not able to see the image falling on it. blind spot blind spot
  • 12. retina ( with light-sensitive cells) We are able to see the image falling on it Why does the ghost disappear?
  • 13. retina ( no light-sensitive cells) We are not able to see the image falling on it
  • 14. We are able to see the images at the same time.
  • 15. We are able to see the images at the same time.
  • 16. The image of ghost is falling on the blind spot, so the ghost disappears. We are able to see the castle only.
  • 17. Do you know why we cannot see the ghost all the way through? Activity Corner D
  • 18. Why don’t we notice the blind spot easily ? Do you know ?
  • 19. Why do we have a pair of eyes but not an eye ? Do you know ?
  • 20. - Lights from objects enter both eyes. As the positions of reflected lights are different , there may be minor differences of the images seen by the two eyes . - The brain combines the two images . => Images with 3-D dimensions => We can judge the distance
  • 21. It shows that we cannot judge distances by using one eye. If you cover an eye , hold a piece of pencil and walk towards another person holding a piece of pencil, can your pencil touch the other one easily ?
  • 22. Many animals have their eyes located at two sides of the head. This can broaden their visions . e.g. elephant, rabbit … But, they do not have 3-D vision . What kinds of animals do not have 3-D vision? Do you know ?