1. Color
Chapter 28

2. The Color Spectrum
Isaac Newton (yeah, him again!) was the first to systematically study color
Spectrum – the spread of all colors, in order: red, orange, yellow, green, blue, and violet
White Light – the combination of all light colors
Black is the absence of light, objects appear black when they have absorbed light of all frequencies
Black objects that you can see do not absorb all light that falls on them, because there is always some reflection off of the surface (you wouldn’t be able to see them without it)

3. Newton’s Color Spectrum

4. Color by Reflection
The colors of most objects around you are due to the way objects reflect light
Electrons can be forced temporarily into larger orbits by the vibrations of electromagnetic waves
Different materials have different natural frequencies for absorbing and emitting radiation
At the resonant frequencies of an object, light is absorbed
If a material absorbs light of most visible frequencies and reflects red, for example, the material will appear red
An object can only reflect light of frequencies present in the illuminating light

5. Color by Transmission
The color of a transparent object depends on the color of the light it transmits
A red piece of glass appears red because it absorbs all the colors that compose white light, except red, which it transmits
Pigment – the material in an object that selectively absorbs colored light
From an atomic point of view, electrons in the pigment atoms selectively absorb light of certain frequencies in the illuminating light

6. Stained Glass Windows

7. Sunlight
White light from the sun is a composite of all the visible frequencies
The brightness of solar frequencies is uneven, red light is not as bright as yellow-green light (humans see yellow-green the best due to this)
The graphical representation of brightness versus frequency is called the radiation curve of sunlight

8. Mixing Colored Light
Light of all the visible frequencies mixed together produces white
White also results from the combination of only red, green, and blue light
When red and green overlap, yellow is produced
When red and blue overlap, magenta is produced
When green and blue overlap, cyan is produced
Additive Primary Colors – red, green, and blue can produce almost any color
Color television is based on the fact that the human eye can see combinations of three colors as a variety of colors

9. Complementary Colors Red + Green = Yellow Red + Blue = Magenta
Blue + Green = Cyan
If you add the third color into these combinations, you will get white light
Complementary Colors – two colors that when added together produce white
Every hue has some complimentary color that when added will produce white
Same concept applies when subtracting colors from white

10. Complementary Colors

11. Mixing Colored Pigments
The mixing of paints and dyes is an entirely different process from the mixing of colored light
Paints and dyes contain finely divided solid particles of pigment that produce their colors by absorbing light of certain frequencies and reflecting light of other frequencies
When we mix colored pigments, we are subtracting the types of colors that the pigment will reflect (color mixing by subtraction), whereas when we mix light, we are adding colors (color mixing by addition)
Subtractive Primary Colors – the three paint colors that are most useful in color mixing by subtraction: magenta, yellow, and cyan

12. Color Subtraction

13. Why the Sky is Blue
Scatter – a redirection of a beam in multiple directions
The nitrogen and oxygen scatter light of higher frequencies more than lower frequencies
Of the visible frequencies, violet light is scattered the most, followed by blue, green, yellow, orange, and red, in that order
Our eyes are more sensitive to blue, so we see a blue sky (not a violet one)
The more larger particles there are in the atmosphere, the less blue the sky appears
The higher you go in the atmosphere, the less particles there are, so the darker the sky is
In a cloud, there are both large and small water droplets, so all frequencies are almost equally scattered, producing a white cloud

14. The Sky and Clouds

15. Why Sunsets are Red
The lower frequencies of light are scattered the least by nitrogen and oxygen molecules; therefore, red, orange, and yellow light are transmitted more readily through the atmosphere
Red light, which is scattered least, passes through more atmosphere without interacting with matter than light of any other color
At dawn and sunset, sunlight reaches us through a longer path through the atmosphere than at noon
The sunlight will look the reddest at these times, at noon it will be more yellow (less atmosphere to travel through

16. Sunset

17. Why Water is Greenish Blue
When we look at the surface of a deep blue ocean or lake, we are actually seeing the color of the reflected sky
The color of water is a pale greenish blue
Water is transparent to nearly all the visible frequencies of light, and the molecules absorb infrared
Water molecules resonate somewhat to the visible-red frequencies, causing a gradual absorption of red light by water and leaving behind red’s complimentary color, cyan
In deep water, many creatures are black or red, both of which cannot be seen easily in the deep waters

18. The Ocean

19. The Atomic Color Code – Atomic Spectra
Every element has its own characteristic color when made to emit light
Spectroscope – instrument used to analyze the light given out by glowing elements
When light from a glowing element is analyzed through a spectroscope, it is found that the colors are a composite of a variety of different frequencies of light
Line Spectrum – the spectrum on an element is not continuous, but appears as separate lines of color, each having a different frequency
The light from each element produces its own characteristic pattern of lines
Much of the information that physicists have about atomic structure is from the study of atomic spectra

20. Atomic Spectra of the Sun

21. Assignment Read Chapter 28 (pg. 421-438)
Do Ch. 28 Assessment #26-45 (pg )