# Group Work Why do cooler objects emit a greater fraction of their energy at long wavelengths (low frequencies)?

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Group Work Why do cooler objects emit a greater fraction of their energy at long wavelengths (low frequencies)?

Light and Color Chapters 26–27

Today’s Objectives Explain how the human eye identifies colors. Explain how colors are produced by absorption, dispersion, and scattering.

How Human Color Vision Works Source: Griffith, Physics of Everyday Phenomena 424530 560

Poll Question What color do we see when green and red receptors are stimulated equally? A. Cyan. B. Blue. C. Yellow. D. Magenta.

Poll Question What color do we see when blue and red receptors are stimulated equally? A. Cyan. B. Blue. C. Yellow. D. Magenta.

Bird and Reptile Color Vision Source: Scientific American, July 2006

Reflection and Transmission (and absorption)

Chlorophyll absorbs blue and red light. What color does it appear? A. red B. yellow C. green D. violet Poll Question

In color printing, which two color inks are combined to make the color orange? Poll Question A.Cyan and Magenta. B.Cyan and Yellow. C.Yellow and Magenta.

Fluorescent Light Not “Natural” Source: www.korry.com/products/nightshield/fluor_light.stm

Colors Split by Dispersion Source: Griffith, Physics of Everyday Phenomena, 4 ed.

Speed in Glass Depends on Index of refraction n = c/v c = vacuum speed v = speed in medium

Poll Question Which is faster in glass? 1.Blue light. 2.Red light. 3.Both have the same speed.

Source: Griffith Prism Separates White Light

Board Work What is wrong with this famous picture?

Dispersion Creates Rainbows Source: Griffith

Primary Rainbow: 1 Reflection Source: Griffith, Physics of Everyday Phenomena 40° 42°

Secondary Rainbow: 2 Reflections Source: Griffith 54.5° 52°

Viewing Both Rainbows Source: Ackerman and Knox, Meteorology

Rayleigh Scattering Why the sky is blue and sunsets are red

Blue Scatters; Red Passes Source: Griffith

Reading for Next Time Atomic Structure –Nuclear composition –Naming isotopes Radioactivity –Nuclear forces –Half-life –Decay types

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