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11.3 Limitations of our eyes

Our eyes have limitations in seeing objects that are too near, too far away, or too small. However, we can overcome these limitations by using suitable instruments. Learn about telescopes, microscopes, and the concept of blind spots in our vision.

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11.3 Limitations of our eyes

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  1. 11.3Limitations of our eyes

  2. - We can see many things, but we cannot see things at all distances or of all sizes. - For people withnormal eyesight, they still have limitations of their eyes.

  3. cannot see / cannot see clearly Limitations of our eyes p.76 1object is too near 2object is too far away 3object is too small

  4. We can overcome some of the limitations by using suitable instruments.

  5. p.77 Activity Corner C 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.

  6. Small objects Distant objects 1 Astronomical telescope 1 2 2 3 3 A B C D E F Electron microscope Telescope Microscope Binoculars Hand lens

  7. Do you know ? p.78 Galileo, an Italian physicist and astronomer, was the first person to point atelescope to the sky. Using his small telescope,Galileo observed the mountains on the Moon.

  8. Hubble Space Telescope is the world’s first space-based optical telescope. How can it ‘take’ the image? Whoorders its jobs? When do the orders send?

  9. Explore the web p.79 Visit the following website to know more about the work of Hubble Space Telescope. http://www.phy.cuhk.edu.hk/phyworld/

  10. Spitzer Space Telescope was named after the great scientist, Lyman Spitzer. How great is he?

  11. Explore the web p.79 Visit the following website to know more about the work of Spitzer and to see more images taken by the Spitzer Space Telescope. http://www.spitzer.caltech.edu/

  12. What is blind spot? Find it out from Activity Corner E 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.

  13. p.80 Activity Corner E 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? ___

  14. We cannot see the object when its image falls on the ___________ of the retina. 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

  15. 3 Repeat the experiment. This time, cover your right eye. Can you see the ghost all the way through? Is there also a blind spot in yourleft eye? _______

  16. blind spot blind spot blind spot (盲點) p.81 - Where the optic nerve leaves the eye - There are no light-sensitive cells => We are not able to see the image falling on it.

  17. Why does the ghost disappear? retina (with light-sensitive cells) We are able to see the image falling on it

  18. retina (no light-sensitive cells) We are not able to see the image falling on it

  19. We are able to see the images at the same time.

  20. We are able to see the images at the same time.

  21. The image of ghost is falling on theblind spot, so the ghost disappears. We are able to see the castle only.

  22. Do you knowwhy we cannot see the ghost all the way through?

  23. Do you know ? Why don’t we notice the blind spot easily?

  24. Do you know ? Why do we have a pair of eyesbut not an eye?

  25. - Lights from objects enter both eyes. As the positions of reflected lights aredifferent, 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

  26. If you cover an eye, hold a piece of pencil and walk towards another person holding a piece of pencil, can your pencil touchthe other one easily? It shows that we cannot judge distances by using one eye.

  27. Do you know ? Many animals have their eyes located at two sides of the head. This can broaden their visions. But, they do not have3-D vision. e.g.elephant, rabbit… What kinds of animals do not have 3-D vision?

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