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LIGHT

LIGHT. Electromagnetic Energy. EM Energy characteristics: Radiant energy Transverse waves Can travel through empty space Speed(c) = 3 x 10 8 m/s Made by vibrating an electron Faster than the Speed of Light???. EM Wavelengths. Light wavelengths are small - measured in “nm”;

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LIGHT

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  1. LIGHT

  2. Electromagnetic Energy • EM Energy characteristics: • Radiant energy • Transverse waves • Can travel through empty space • Speed(c) = 3 x 108 m/s • Made by vibrating an electron • Faster than the Speed of Light???

  3. EM Wavelengths • Light wavelengths are small - measured in “nm”; • Metric prefix – “n” = ???? • But… λ must be in “meters” to use v = fλ • Ex: Violet light has a wavelength of 400 nm. How many meters is this? What is the frequency of violet light? • 400 nm = 400 x 10-9 m • v = fλ • 3 x 108 = (f)(400 x 10-9) • f = 7.5 x 1014 Hz

  4. Electromagnetic Spectrum Radioactive Martians Invade Venus Using X-ray Guns Visible: 750 to 400 nm Low frequency = long λ = low energy High frequency = short λ = high energy

  5. Electromagnetic Spectrum Increasing Energy Increasing Frequency 700 400

  6. Not all light is visible! • RMIVUXG • Red Martians Invaded Venus Using X-ray Guns Increasing Energy Increasing Frequency

  7. BEHAVIORS OF LIGHT

  8. Behaviors of Light • Light can behave in one of two ways: • As a WAVE • Five wave behaviors • As a PARTICLE • Two particle behaviors • Let’s explore the WAVE behaviors of light first…..

  9. WAVE Behaviors of Light • Five Wave Behaviors of Light • Reflection • Refraction • Diffraction • Interference • Polarization How do we see light?

  10. Wave Behaviors of Light – 1. REFLECTION • Reflection – bouncing of light • Ex: Mirrors • Law of Reflection: • Θi= Θr • Angles measured in reference to a line that is perpendicular to the surface called the Normal

  11. Wave Behaviors of Light – 1. REFLECTION • Law of Reflection Why is it dark at night? Reflected ray Incident ray Normal Θi Θr

  12. Water Wave Behaviors of Light – 2. REFRACTION • Refraction – bending of light • Change in path due to change in speed • Change in speed caused by change in medium that light is traveling through • Ex: pencil in cup of water looks “bent” Air

  13. Wave Behaviors of Light – 2. REFRACTION Snell’s Law: n1•sin θ1 = n2 • sin θ2

  14. Wave Behaviors of Light – 3. DIFFRACTION • Diffraction – spreading out of light • Diffraction grating disperses light into its component colors • Ex: hologram on credit card • colors seen on CD / DVD face

  15. Wave Behaviors of Light – 3. DIFFRACTION

  16. Wave Behaviors of Light – 4. INTERFERENCE • Interference – Constructive or destructive • Results in light/dark patterns • Ripple Tank The Original Double Slit Experiment

  17. Wave Behaviors of Light – 4. INTERFERENCE

  18. Wave Behaviors of Light – 4. INTERFERENCE

  19. Wave Behaviors of Light – 4. INTERFERENCE

  20. Wave Behaviors of Light - 5. POLARIZATION • Polarization – light waves vibrating in one plane only • Light from sun is non-polarized • Polarizing filter lets only one vibration through, blocks all others • HEWITT image, p. 578 sunlight filter Only vertically vibrating light can get through If a second filter is placed on top of the first no light gets though

  21. Behaviors of Light • Light can behave in one of two ways: • As a WAVE • Five wave behaviors • As a PARTICLE • Two particle behaviors • Now let’s look at the PARTICLE behaviors of light…..

  22. PARTICLE Behaviors of Light • Two Particle Behaviors of Light • Photoelectric Effect • Atomic Line Spectra

  23. Particle Behaviors of Light – 1. PHOTOELECTRIC EFFECT • When light shines on a piece of metal, electricity flows • 1) Since electricity = flow of electrons, and 2)electrons are matter, 3) Waves don’t transfer matter, just energy! • Youcannot use the wave behavior of light to explain this! • (?) • Therefore, light must be made of particles called PHOTONS • Photon – a massless particle of light that has a specific amount of energy associated with it, depending on the frequency (color) of the light

  24. Particle Behaviors of Light – 1. PHOTOELECTRIC EFFECT Phet Photoelectric effect

  25. Particle Behaviors of Light – 2. ATOMIC LINE SPECTRA • Electron is hit by a photon • Absorbs the energy from the photon • Electron with more energy moves up to higher energy level • When electron “decays” back to lower energy level, it releases a photon • Released photons emit light – we see this light as specific colors • These energy level jumps are called quantum leaps • http://phet.colorado.edu/simulations/sims.php?sim=Models_of_the_Hydrogen_Atom

  26. The light at the end of the lecture….. • LIGHT HAS A DUAL NATURE….IT IS BOTH A WAVE AND A PARTICLE!!!

  27. Now let’s talk about color…

  28. Part I - Clays http://www.omsi.info/visit/tech/colormix.cfm Color wheel • Magenta + Cyan = • Cyan + Yellow = • Yellow + Magenta = • Magenta + Yellow + Cyan = • Why isn’t the 3-color combo black? • What are the primary pigments? • Are the primary pigments what you expected them to be? Blue Green Red Brown • Need to mix EXACTLY the same proportions of colors • Cyan is a little too dark • Magenta, Yellow, and Cyan

  29. Part II - Spotlights Yellow Cyan Magenta White Light Color Wheel Pigment Color Wheel Magenta Red M B R Y W Blk Green Blue G C Cyan Yellow

  30. Questions • What is the difference between light and pigments? • What are the primary colors of light? • What are the secondary colors of light? • How do the primary and secondary colors of light compare to the primary and secondary colors pigments? • How do you make white light? How do you make black light? • How do you make white pigment? How do you make black pigment? • light is color from rays, pigment is a dye in materials • RGB – red, green, blue • MYC – magenta, yellow, cyan • opposites • combine equal parts RGB; remove light • remove pigments; combine equal parts MYC

  31. Color • http://micro.magnet.fsu.edu/primer/java/scienceopticsu/newton/ • Isaac Newton was the first scientist to make a systematic study of color. By passing a beam of sunlight through a prism, he showed that the light could be separated into the colors of the spectrum: ROY G BIV • White is not a color - it is all the colors combined. • Black is not a color either - it is the absence of color.

  32. Color By Reflection • The colors of most objects are due to the way that they reflect light. • Different materials and dyes absorb some colors of light and reflect others. The color that the object appears is the color of light that is reflected by the object. Flower absorbs B, Leaf absorbs R&B light White light (RGB) Absorbs G&B light White light (RBG) Flower reflects R&G light Reflects R light Leaf reflects G light

  33. What if you put the plant under magenta light instead? Magenta light (B&R) Flower absorbs B, Leaf absorbs R&B light Flower reflects Red light Leaf reflects nothing – black!

  34. Three Color Theory • 3 types of nerves (cones) in the retina interpret the primary colors of light (Red, Green, and Blue.) Our brains interpret the signals from these nerves to determine the “color” of an object. • Combining 2 primary colors of light will give a secondary color: • Red + Green = • Blue + Green = • Red + Blue = • Red + Blue + Green = Yellow Cyan Magenta White

  35. Practice • What color does each of these objects appear? What do they absorb? White light White light Red Blue Appears Y, absorbs B Appears M, absorbs G Red Green You want a black room, but your mom doesn’t want to use three coats of primer to get rid of it when you go to college. What color light bulb can you use to make the cyan paint APPEAR black? White light Red White light Green Appears white, absorbs nothing Green Blue Red Blue Appears C, absorbs R

  36. Practice • What color is produced by mixing the following colors of light? • Yellow + Blue = • Magenta + Green = • Cyan + Red = White White White

  37. Complementary Colors • Whenever a primary color of light is mixed with its complementary secondary color, white light will be produced. • They are opposites on the color wheel • Combos are thought to “match” Magenta Cyan Yellow

  38. Pigments – Subtractive Color Formation • Pigments are colored materials that absorb certain colors and reflect others • They are present in dyes, paints, inks, etc. • Primary pigments absorb one color of light. Blue Green Red Magenta Blue Green Red Cyan Blue Green Yellow Red

  39. Pigments – Subtractive Color Formation • Secondary pigments absorb two colors of light. Blue Green Red Red Green Blue Green Red Blue Blue Green Red

  40. Practice • What color would appear if the following pigments were mixed? • Yellow + cyan = • Cyan + magenta = • Magenta + yellow = • Magenta + green = • Cyan + red = • Cyan + magenta + yellow = • Whenever a primary pigment is mixed with its complementary secondary pigment, the color produced will be: Green Blue Red Black Black Black Black

  41. Check for understanding • Why are the insides of binoculars and cameras painted black? • You put a piece of red cellophane over one flashlight and a piece of green cellophane over another. You shine the light beams on a white wall. What color will you see where the two beams overlap? • You now put both the red and green cellophanes over one flashlight. If you shine the flashlight beam on a white wall, what color do you see? Explain. • Black absorbs all color, so no light bounces off the sides of the lens and distorts the image. • Yellow • Black. The white light goes through the red cellophane, which filters out G&B leaving only red light. Then the green cellophane filters out the red light, leaving no light to go through.

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