# Chapter 14 Light and Color.

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Chapter 14 Light and Color

14.1 Electromagnetic Spectrum
Figure 14.3 If strike charged metal to and fro in empty space, get electromagnetic waves Classification of electromagnetic waves according to frequency- electromagnetic spectrum 0.01 Hz to 1 MHz (AM radio) or VHF (very high frequency for tv), 88 to 108 MHz for FM radio, UHF (ultra high frequency, microwaves Lowest visible = red, highest = violet Low frequency = long wavelength, high frequency = short wavelength

14.2 Transparent vs. Opaque When light passes through, electrons in matter forced to vibrate (emitter to receiver, like sound) Pass in straight lines- transparent Why? Spring strengths- glass vibrates in UV, so when UV goes through glass, have resonance and builds amplitude, re-emitted energy (glass is not transparent to UV) Less amplitude with lower frequency, so not as many collisions, less heat, re-emitted light = initial frequency, just time delay

Speed of light 3x10^8 m/s = c in vacuum 0.75c in water 0.67c in glass
0.41c in diamond

Opaque Most objects Absorb light without re-emitting
Vibrations are made into thermal energy Metals have no “spring” and energy is reflected (shine) Some UV, all Vis, some IR transparent, but high frequency (crispy) UV is opaque for atmosphere Why darker when wet? Dry bounces directly to eye, wet has to go underneath surface first to bounce, and each bounce is absorption

14.3 Color Science Color is in the eye of the beholder (color blind)
Depends on frequency (ROY G BIV) Selective Reflection- absorb light, only reflect apparent color (white vs. black in science, art) Daffodils reflect red, green, yellow Depends on light shining on object (fluorescent-blue) Selective transmission- color of transparent objects depends on color of light transmitted, have pigments- particles that choose the light to absorb/transmit

14.4 Mixing Colored Lights White light- rainbow in prism
Solar- yellow green (we’re most sensitive) All colors make white Primary colors= red, blue, green (tv tube) Red and blue make magenta, red and green make yellow, blue and green make cyan (complementary colors) Magenta + green, yellow + blue, cyan + red = white Printer inks need complementary colors and black

14.5 Mixing Colored Pigments
Red, green, blue paint= brown Pigments absorb specific colors (red absorbs cyan, or subtracts it from white) Magenta, cyan, yellow= subtractive primaries

14.6 Why Sky is Blue Selective scattering- light far apart
Violet scattered most (reverse Roy G Biv), but eyes not sensitive to violet light, so see most blue Less water vapor, more blue, whitish when stormy, gray smog

14.7 Why Sunsets are Red ROY least scattered, better transmitted
Thicker atmosphere, more time to scatter, so red travels best, path longer later in the day (lower sun), scatters more violet and blue, removal of complementary (violet and orange, green and magenta, blue and yellow)

14.8 Why Clouds are White Clouds made of water droplets of different sizes that scatter a variety of colors Tiny clusters- blue clouds, medium = green, large = red Cluster vibrations make brightness (crowd shouting louder than one person) Absorb more, darker, have rain with large clusters