11.3 Limitations of our eyes
-  We  can see  many things, but we  cannot see  things at  all distances  or of  all sizes . -  For people with   normal ...
1   object is  too near p.76 Limitations  of our eyes   2   object is  too far away 3   object is  too small cannot see  /...
We can overcome  some of the  limitations  by using suitable  instruments.
p.77 Extending our vision Separate the following  instruments  into  two groups  according to  their functions  and arrang...
A B C D E F Microscope Telescope Binoculars Electron microscope Hand lens Distant objects Small objects 1  Astronomical  t...
We cannot see clearly when the object is  too small, too near or too far away.  There is another limitation of our eyes  ...
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 ...
2  Repeat step 1. This time,  keep looking at the cross  while you  slowly move the book towards you . Can you see the gho...
Is there also a  blind spot  in your   left eye?  _______ 3  Repeat the experiment. This time,  cover your right eye.  Can...
p.81 blind spot  ( 盲點 )   -  Where the  optic nerve  leaves the eye -  There are  no  light-sensitive cells =>  We are  no...
retina   ( with  light-sensitive cells) We are able to  see  the image  falling on  it Why does the ghost disappear?
retina   ( no  light-sensitive cells) We are  not  able to  see  the image  falling on  it
We are able to  see  the images  at the same time.
We are able to  see  the images  at the same time.
The  image of ghost  is falling on the   blind spot,  so the ghost disappears.  We are able to  see  the castle  only.
Do you know   why  we cannot see the  ghost  all the way through? Activity Corner D
Why don’t we  notice  the  blind spot  easily ? Do you know ?
Why do  we have  a pair of eyes   but not  an eye ?   Do you know ?
-  Lights  from objects enter both eyes.  As  the positions  of reflected lights are   different , there may be  minor dif...
It shows that we  cannot  judge  distances  by using one eye. If you  cover an eye , hold  a piece of pencil  and walk tow...
Many animals have their eyes located at  two sides of the head.  This can  broaden their visions . e.g.   elephant, rabbit...
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11.3e

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11.3e

  1. 1. 11.3 Limitations of our eyes
  2. 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. 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. 4. We can overcome some of the limitations by using suitable instruments.
  5. 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. 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. 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. 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. 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. 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. 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. 12. retina ( with light-sensitive cells) We are able to see the image falling on it Why does the ghost disappear?
  13. 13. retina ( no light-sensitive cells) We are not able to see the image falling on it
  14. 14. We are able to see the images at the same time.
  15. 15. We are able to see the images at the same time.
  16. 16. The image of ghost is falling on the blind spot, so the ghost disappears. We are able to see the castle only.
  17. 17. Do you know why we cannot see the ghost all the way through? Activity Corner D
  18. 18. Why don’t we notice the blind spot easily ? Do you know ?
  19. 19. Why do we have a pair of eyes but not an eye ? Do you know ?
  20. 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. 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. 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 ?

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