Chapter 6: Light and Color in Nature What is a mirage? How do rainbows form? Why is the sky blue and...
-
Upload
phoebe-elliott -
Category
Documents
-
view
215 -
download
0
Transcript of Chapter 6: Light and Color in Nature What is a mirage? How do rainbows form? Why is the sky blue and...
![Page 1: Chapter 6: Light and Color in Nature What is a mirage? How do rainbows form? Why is the sky blue and sunset red?](https://reader035.fdocuments.in/reader035/viewer/2022062515/56649ced5503460f949bad7a/html5/thumbnails/1.jpg)
Chapter 6: Light and Color in Nature
What is a mirage?
How do rainbows form?
Why is the sky blue and sunset red?
![Page 2: Chapter 6: Light and Color in Nature What is a mirage? How do rainbows form? Why is the sky blue and sunset red?](https://reader035.fdocuments.in/reader035/viewer/2022062515/56649ced5503460f949bad7a/html5/thumbnails/2.jpg)
Light & Color in Nature
Refraction effects:
MiragesRainbowsHalos
Interference effects:
Oil films / soap bubblesIridescence
Scattering effects:
Blue sky / sunsets
![Page 3: Chapter 6: Light and Color in Nature What is a mirage? How do rainbows form? Why is the sky blue and sunset red?](https://reader035.fdocuments.in/reader035/viewer/2022062515/56649ced5503460f949bad7a/html5/thumbnails/3.jpg)
Atmospheric Refraction
•Air density (refractive index) varies due to pressure or temperature.
•Light rays refract (bend) toward the denser medium. This causes mirages or flattening of the sun at sunset time.
Warmer air orlow pressure
Cooler air orhigh pressure
![Page 4: Chapter 6: Light and Color in Nature What is a mirage? How do rainbows form? Why is the sky blue and sunset red?](https://reader035.fdocuments.in/reader035/viewer/2022062515/56649ced5503460f949bad7a/html5/thumbnails/4.jpg)
Flattening of the Sun
The sun is visible before the sunrise and after the sunset making the days longer!
![Page 5: Chapter 6: Light and Color in Nature What is a mirage? How do rainbows form? Why is the sky blue and sunset red?](https://reader035.fdocuments.in/reader035/viewer/2022062515/56649ced5503460f949bad7a/html5/thumbnails/5.jpg)
Inferior Mirage
![Page 6: Chapter 6: Light and Color in Nature What is a mirage? How do rainbows form? Why is the sky blue and sunset red?](https://reader035.fdocuments.in/reader035/viewer/2022062515/56649ced5503460f949bad7a/html5/thumbnails/6.jpg)
Inferior Mirage (Contd.)
Image appears below the object giving the illusion of water!
![Page 7: Chapter 6: Light and Color in Nature What is a mirage? How do rainbows form? Why is the sky blue and sunset red?](https://reader035.fdocuments.in/reader035/viewer/2022062515/56649ced5503460f949bad7a/html5/thumbnails/7.jpg)
Superior Mirage
![Page 8: Chapter 6: Light and Color in Nature What is a mirage? How do rainbows form? Why is the sky blue and sunset red?](https://reader035.fdocuments.in/reader035/viewer/2022062515/56649ced5503460f949bad7a/html5/thumbnails/8.jpg)
Superior Mirage (Contd.)
Image appears above the object giving the illusion of taller image or image floating in the sky!
![Page 9: Chapter 6: Light and Color in Nature What is a mirage? How do rainbows form? Why is the sky blue and sunset red?](https://reader035.fdocuments.in/reader035/viewer/2022062515/56649ced5503460f949bad7a/html5/thumbnails/9.jpg)
Rainbows: Refraction by Water Droplets
Alexander’s dark band
Primary bow(brighter)Secondary bow
(dimmer)
![Page 10: Chapter 6: Light and Color in Nature What is a mirage? How do rainbows form? Why is the sky blue and sunset red?](https://reader035.fdocuments.in/reader035/viewer/2022062515/56649ced5503460f949bad7a/html5/thumbnails/10.jpg)
Rainbows: Refraction by Water Droplets
http://www.phy.ntnu.edu.tw/ntnujava/viewtopic.php?t=61
•Formed by “class 3” rays.•Brighter with red on top.•Cannot be observed if sun is higher than 420 above the horizon.
Primary
•Formed by “class 4” rays.•Less bright with blue on top.•Cannot be observed if sun is higher than 520 above the horizon.
Secondary
![Page 11: Chapter 6: Light and Color in Nature What is a mirage? How do rainbows form? Why is the sky blue and sunset red?](https://reader035.fdocuments.in/reader035/viewer/2022062515/56649ced5503460f949bad7a/html5/thumbnails/11.jpg)
Rainbows: Other Features
Alexander’s Dark Band:
No refraction is possible between 420 and 520 rainbows.
Supernumerary Arcs:
Pink & green bands below the primary bow. Produced by interference between sun rays.
![Page 12: Chapter 6: Light and Color in Nature What is a mirage? How do rainbows form? Why is the sky blue and sunset red?](https://reader035.fdocuments.in/reader035/viewer/2022062515/56649ced5503460f949bad7a/html5/thumbnails/12.jpg)
Refraction Through Ice Crystals: Halos
Hexagonal (pencil shaped) ice crystals are formed in high cirro-stratus clouds. These ice crystals can refract light into two concentric circles (halos) depending on how they are oriented.
http://www.atoptics.co.uk/
http://www.snowcrystals.com/
![Page 13: Chapter 6: Light and Color in Nature What is a mirage? How do rainbows form? Why is the sky blue and sunset red?](https://reader035.fdocuments.in/reader035/viewer/2022062515/56649ced5503460f949bad7a/html5/thumbnails/13.jpg)
Refraction Through Ice Crystals: Halos
Parhelia (sun dogs)
Upper tangent arc
220 Halo
460 Halo
![Page 14: Chapter 6: Light and Color in Nature What is a mirage? How do rainbows form? Why is the sky blue and sunset red?](https://reader035.fdocuments.in/reader035/viewer/2022062515/56649ced5503460f949bad7a/html5/thumbnails/14.jpg)
Interference Effects: Oil Films and Soap Bubbles
•Thin transparent layer sandwiched between two transparent media.
•Reflected waves can be in-phase or out-of-phase depending on the film thickness and its refractive index.
•If white light is incident, some colors will interfere destructively. Thin film acts like a filter!
http://micro.magnet.fsu.edu/primer/java/interference/soapbubbles/index.html
![Page 15: Chapter 6: Light and Color in Nature What is a mirage? How do rainbows form? Why is the sky blue and sunset red?](https://reader035.fdocuments.in/reader035/viewer/2022062515/56649ced5503460f949bad7a/html5/thumbnails/15.jpg)
Scattering Effects
Lunar sky looks black because there is no atmosphere to scatter light!
Scattering of light occurs when a beam of light is broken into several smaller, less intense beams of light by gases, aerosols, or particulates in the atmosphere.
![Page 16: Chapter 6: Light and Color in Nature What is a mirage? How do rainbows form? Why is the sky blue and sunset red?](https://reader035.fdocuments.in/reader035/viewer/2022062515/56649ced5503460f949bad7a/html5/thumbnails/16.jpg)
Rayleigh Scattering
• Small particles of size 50 – 100 nm scatter light with an efficiency:
•“Shorter” wavelengths are scattered more efficiently.
4
1
se
At sunset or sunrise light travels a greater distance through the atmosphere, thereby allowing moreof the blue light to be scattered. That’s why the sky appears blue and the setting sun appears red.
![Page 17: Chapter 6: Light and Color in Nature What is a mirage? How do rainbows form? Why is the sky blue and sunset red?](https://reader035.fdocuments.in/reader035/viewer/2022062515/56649ced5503460f949bad7a/html5/thumbnails/17.jpg)
Scattering Effects (Contd.)
Mie Scattering: Large particles (steam, clouds…) scatter all wavelengths equally well giving a milky white appearance.
Clouds
Glacial water
![Page 18: Chapter 6: Light and Color in Nature What is a mirage? How do rainbows form? Why is the sky blue and sunset red?](https://reader035.fdocuments.in/reader035/viewer/2022062515/56649ced5503460f949bad7a/html5/thumbnails/18.jpg)
Trivia
Why are the taxiway lights violet and runway lights amber? Why is red used to signal danger?
Red suffers the least atmospheric scattering so it can be seen from far away.
![Page 19: Chapter 6: Light and Color in Nature What is a mirage? How do rainbows form? Why is the sky blue and sunset red?](https://reader035.fdocuments.in/reader035/viewer/2022062515/56649ced5503460f949bad7a/html5/thumbnails/19.jpg)
Review Problems
1. In Rayleigh scattering, how much more efficiently is light of 420 nm scattered than light of 650 nm?
2.Suppose the earth’s atmosphere scatters 10% of the incident blue light, 5% of green and 1% of red light for every mile the light travels through it. 100 units each of R, G, and B lights are incident on it from the sun. Calculate how many units of each wavelength remain after the light has traveled 1 mile, 2 miles, 3 miles… through the atmosphere?
5.7 times
After 1 mile: R=99, G=95, B=90After 2 miles: R=98, G=90, B=81…