1. Optical fibers and “light tubes” rely on total internal reflection
Can transmit light signals for hundreds of km without much loss.

2. Imaging optical fiber bundles
An ordered array of thousands of fibers…very expensive. Each fiber is a pixel. But cameras can be made small to replace these.

3. Mirages

4. Air index is lowest near the hot ground
Imagine the air made of many layers of different n. Ray turns away from normal. At some point it is totally internally reflected, then turns toward normal

5. P1. An object is a distance of 1km (essentially infinity) to the left of a lens of focal length 10 cm. The image is ______ from the lens. a) 1 cm b) 2 cm c) 4 cm d) 5 cm e) 10 cm P2. A second identical lens is placed 5cm to the right of the first lens. The final image is at a distance of _____ cm from lens 2. A B C D E Is it to the right or left of the second lens?

6. What part does the major focusing: … the fine tuning: How well do your eyes work in water? Lasik surgery

7. A real inverted image is formed on the retina…but our brains see that as upright.

8. Accomodation
For different object distances, the “lens” tries to adjusts f so image is always on the back of the eye.
Relaxed normal eye:
f = length of eye (for far objects)
“Far point” for normal eye: infinity
Strained normal eye:
f decreases (for near objects).
“Near point” for normal eye is about 25 cm. object distance.

9. Combining two or more adjacent lenses into one focal length
Opticians use diopters (1/meters) to describe the focusing (defocusing) “power” of lenses.

10. Combining two or more adjacent lenses into one focal length
Find the power of the relaxed eye. Find the largest power of the strained eye.

11. Nearsighted eye
Simplest description of problem: The “far point” of this eye is bad: closer than infinity.
Simplest description of solution: Put a diverging lens so that an object at infinity will make a virtual image at the “bad far point”. This the eye can see.

12. Farsighted eye
Simplest description of problem: The “near point” of this eye is bad: farther than 25 cm.
Simplest description of solution: Put a converging lens so that an object at 25 cm will make a virtual image at the “bad near point”. This the eye can see.

13. Fun eye test for near-sightedness

14. P3. A patient has far point of 10 m
P3. A patient has far point of 10 m. What is the focal length of a lens that will correct this? ____m
a) -10 b) -5 c) 5 d) 10
P4. A patient has near point of 1 m. What is the focal length of a lens that will correct this? ____m
a) b) c) 0.33 d) 0.25

15. How to replace bifocals
Make a lens that changes its index rather than curvature in different areas. Merge different plastics together.

16. Astigmatism
When the eye is not circular about its axis. Is one direction of lines sharper?
Correction: Add cylindrical len component to the corrective lens

17. Magnifying glass
The problem with trying to see small things is that we can’t see them closer than our near point. To get more detail, we use a lens and make do <f. Then we see a larger virtual image at our near point or farther. do

18. Microscope: Object near first lens, so first image is beyond fo
Microscope: Object near first lens, so first image is beyond fo. Look at that with eyepiece. Two short f’s used. Telescope: Object very far away so first image is at fo. Look at that with eyepiece. One long, one short f’s used. In both cases, the eyepiece is adjusted so the first image less than fe away, so the eye can see a final virtual image, which is far enough away so the eye can be relaxed.

19. Why the sky is blue?
Why are sunsets red and orange?

20. Why the sky is blue?
Rayleigh scattering occurs when particle size << l.
Sunlight scatters weakly off air molecules. This scattering is most efficient at ________ frequencies or _________ wavelengths!

21. Why do so many powdered things and clouds look white?
Salt
When any non absorbing material (glass, water, salt) is broken into pieces of size >l they scatter all wavelengths equally, which is “white”. This is called Mie scattering.

22. Why do so many powdered things and clouds look white?
Paper fibers are transparent under microscope

23. Tobacco smoke is bluish, yet when he blows it out, it’s white
Tobacco smoke is bluish, yet when he blows it out, it’s white. What’s happened?

24. Vector nature of color
“Spectral” (rainbow) colors are those perceived from light of narrow band of w,l.

25. All colors are not in the rainbow
Explain why brown e.g.
[4, 2, 1] can’t be in the rainbow

26. Additive coloring : (light emission, screens, projection)
Can create any color by superimposing three primary colors with varying intensities.
Requirements for primary spectral colors?

27. Subtractive coloring
uses dyes, inks, and pigments to absorb some wavelengths of light and not others.
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