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Light Fundamentals

Chapter 16. Light Fundamentals. The Dual Nature of Light. Is light a particle or a wave? Turns out it acts like both. Photons are packets of light energy Photons travel in waves Look at the wave nature of light so we can predict how it will behave, where it will go or where it came from.

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Light Fundamentals

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  1. Chapter 16 Light Fundamentals

  2. The Dual Nature of Light • Is light a particle or a wave? • Turns out it acts like both. • Photons are packets of light energy • Photons travel in waves • Look at the wave nature of light so we can predict how it will behave, where it will go or where it came from. • So if light is a wave, what’s waving?

  3. Light & Matter • What gives us light? • Electrons moving from an excited to ground state. • A few definitions: • Transparent • Can see through it (i.e. windows) • Translucent • Can see through it but not clearly (frosted glass) • Opaque • Cannot see through it

  4. Note: • We will not be “quantifying” light so you will not be held responsible for the definitions of luminous flux, illuminance, or luminous intensity.

  5. Speed of Light • Galileo • Hypothesized that light had a definite speed but it was too fast to measure (earlier it was thought that light traveled instantaneously). • Ole Roemer (1644-1710) • Trying to improve maps . Measured the orbital period of Io, one of the moons of Jupiter, and found it was shorter when Earth was approaching Jupiter and longer when Earth was moving away from Jupiter… now knew that light had a definite speed (but his calculations weren’t great).

  6. Albert Michelson (1852-1931)

  7. Albert Michelson • First American to win the Nobel Prize (1907) • Found the speed of light to be 3.00 x 108 m/s • What is a light year? • Know d = vt = 3.00 x 108 m/s (1 year) = 9.5 x 1012 km • So it’s a measure of distance.

  8. Diffraction Revisited • The bending of light as it passes the edge of a barrier. • Remember the pattern created by the double slit barrier in the Ripple Tank Lab?

  9. Electromagnetic Spectrum • Light is energy emitted by vibrating electric charges in atoms. • Visible light is a small portion of the entire spectrum.

  10. Color of light is related to wavelength • Longer wavelengths of light bend more than shorter wavelengths. • Can get a spectrum when light is shined through a prism. • Glass bends the light and it separates according to wavelength.

  11. Primary Colors • Add together to get white • Red, Blue, Green • When light colors are added, get the secondary colors of light G+B = cyan B+R = Magenta R+G = Yellow Low f Mid f High f

  12. How We Perceive Color • Our eyes are only sensitive to R,G,B light • We take the stimuli from those three colors and interpret all the other colors based on the proportion of RGB. • White light can be described as a combination of RGB • Printed materials use the secondary colors (C,Y,M) + black to print colored materials.

  13. See Acetate Demo on Overhead… • With three colors of pigment (C.Y,M) and black, you can create any color in print.

  14. + = Add black and get… = +

  15. Complementary Colors • Complementary Colors • Two colors that add together to give white • Yellow + Blue • Cyan + Red • Magenta + Green • Fun fact: Older TVs are made up of R,G,B spots. Turning on and off gives all colors.

  16. Remember This • If all colors are reflected back to our eyes, we see white. • If no color is reflected back, we see black.

  17. Color Subtraction – What you learned in kindergarten. • Dyes – molecules that absorb certain wavelengths and transmit or reflects others. We see what is reflected. • Pigment – Acts as a dye but larger molecules. • Primary Pigments – Pigments which absorb only one color of white light • Yellow pigment – absorbs blue light • Cyan pigment – absorbs red light • Magenta pigment – absorbs green light

  18. Color Subtraction – Cont’d • Secondary Pigments – absorb two colors of primary light and reflect one. • Red – absorbs green and blue • Green – absorbs red and blue • Blue – absorbs red and green • How to get green paint: ROYGBIV – blue pigment (absorbs ROY, reflects BIV) ROYGBIV – yellow pigment (absorbs BIV, reflects ROY) Green is the only color reflected by both colors of paint.

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