SCI 340 L51 Light and color not really in your book This lecture takes lots of demonstration apparatus: Transmission overhead projector with Diffraction grating after focusing lens Slit mask Square mask CMY filters RGB filters RGB filter wheels Vertical-slit lamp and variac Class set of diffraction gratings R, G, B projectors not really in your book

Today’s Objectives Explain how the human eye identifies colors. SCI 340 L51 Light and color Today’s Objectives Explain how the human eye identifies colors. Explain how colors are produced by absorption, dispersion, and scattering.

Electromagnetic Wave Energy General Physics L19_EMwaves Electromagnetic Wave Energy Non-classical result: E = hf E = energy f = frequency h = Planck constant = 6.621  10-34 J s

General Physics L19_EMwaves

Temp Influences Spectrum General Physics L19_EMwaves Temp Influences Spectrum Higher T  greater power P/A = sT4 s = 5.6710–8 W m–2 K–4 Higher T  higher peak frequency lmax = b/T b = 2.898 106 nm K Demonstrate Vertical slit with variac, students each have diffraction grating. Show that light is dimmer and redder at lower temperatures. Source: M. A. Seeds, Exploring the Universe

SCI 340 L51 Light and color Group Work Why do cooler objects emit a greater fraction of their energy at long wavelengths (low frequencies)?

How Human Color Vision Works SCI 340 L51 Light and color How Human Color Vision Works 424 530 560 Demonstrate R, G, B slide projectors. Secondary colors formed from primaries, white from combination of all three. Source: Griffith, Physics of Everyday Phenomena

SCI 340 L51 Light and color Poll Question What color do we see when green and red receptors are stimulated equally? A. Cyan. B. Blue. C. Yellow. D. Magenta.

SCI 340 L51 Light and color 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 SCI 340 L51 Light and color Bird and Reptile Color Vision Source: Scientific American, July 2006

Reflection and Transmission SCI 340 L51 Light and color Reflection and Transmission Demonstrate Color filters R, G, B, C, M, Y with overhead projector slit and diffraction grating. Filters Remove colors from light. Subtractive primary colors C, M Y with square mask and no diffraction grating on the projector. Combinations create additive primary colors and black. (and absorption)

SCI 340 L51 Light and color Poll Question Chlorophyll absorbs blue and red light. What color does it appear? A. red B. yellow C. green D. violet

SCI 340 L51 Light and color Poll Question In color printing, which two color inks are combined to make the color orange? Cyan and Magenta. Cyan and Yellow. Yellow and Magenta. Demonstrate with CMY color wheel. Removing the C wheel still leaves a position of orange.

Fluorescent Light Not “Natural” SCI 340 L51 Light and color Fluorescent Light Not “Natural” Source: www.korry.com/products/nightshield/fluor_light.stm

Colors Split by Dispersion SCI 340 L51 Light and color Colors Split by Dispersion Source: Griffith, Physics of Everyday Phenomena, 4 ed.

Speed in Glass Depends on l SCI 340 L51 Light and color Speed in Glass Depends on l Index of refraction n = c/v c = vacuum speed v = speed in medium

Poll Question Which is faster in glass? Blue light. Red light. SCI 340 L51 Light and color Poll Question Which is faster in glass? Blue light. Red light. Both have the same speed.

Prism Separates White Light SCI 340 L51 Light and color Prism Separates White Light Source: Griffith

Board Work What is wrong with this album cover? SCI 340 L51 Light and color Board Work What is wrong with this album cover?

Dispersion Creates Rainbows SCI 340 L51 Light and color Dispersion Creates Rainbows Source: Griffith

Primary Rainbow: 1 Reflection SCI 340 L51 Light and color Primary Rainbow: 1 Reflection 40° 42° Source: Griffith, Physics of Everyday Phenomena

Secondary Rainbow: 2 Reflections SCI 340 L51 Light and color Secondary Rainbow: 2 Reflections 54.5° 52° Source: Griffith

Viewing Both Rainbows Source: Ackerman and Knox, Meteorology SCI 340 L51 Light and color Viewing Both Rainbows Source: Ackerman and Knox, Meteorology

SCI 340 L51 Light and color Why the sky is blue and sunsets are red Rayleigh Scattering Why the sky is blue and sunsets are red

SCI 340 L51 Light and color There probably isn’t time, but this can be demonstrated nicely with a white light beam shining through dilute milk. The scattered light is bluish and the transmitted light is reddish.

Blue Scatters; Red Passes SCI 340 L51 Light and color Blue Scatters; Red Passes Source: Griffith

Next Time Ray optics Ray tracing for mirrors Formulas for mirrors Ray tracing for lenses Formulas for lenses