2. Physics 1230: Light and Color Ivan I. Smalyukh, Instructor Office: Gamow Tower, F-521 Email: ivan.smalyukh@colorado.edu Phone: 303-492-7277 Lectures: Tuesdays & Thursdays, 3:30 PM - 4:45 PM Office hours: Mondays & Wednesdays, 3 PM - 4 PM Grading Assistants: Jian Yao, Yiheng Lin, Hao Song Lectures Homeworks Exams Hands-on experience Demonstrations Peer Instruction (with extra credit) Fun

3. 2 WebsiteWebsite http://www.colorado.edu/physics/phys1230/phys1230_fa09/ SyllabusSyllabus –Science of light and color –HW assignments, reading and exam dates Course infoCourse info –Grades –Clicker technology Another kind of invisible waveAnother kind of invisible wave WebsiteWebsite http://www.colorado.edu/physics/phys1230/phys1230_fa09/ SyllabusSyllabus –Science of light and color –HW assignments, reading and exam dates Course infoCourse info –Grades –Clicker technology Another kind of invisible waveAnother kind of invisible wave Course Business

4. Physics 1230: Light and Color Ivan I. Smalyukh What is "science"? Why is learning science like learning a foreign language? –Words have new and precise meanings –Wave, image, ray, lens, white, exposure, file, see, reflection, refraction, dispersion, particle –What does it mean for the "sun to set?" Is there really global warming? How could complex and magnificent creatures like us have evolved from lower species? We all have scientific curiosity: Why the sky is blue? What is rainbow? What is sunset? How my laptop display works? We all have scientific curiosity: Why the sky is blue? What is rainbow? What is sunset? How my laptop display works?

7. Ornithoptera chimaera chimaera Ornithoptera goliath supremus, f. titan Ornithoptera priamus urvillianus Papilio blumei blumei

11. What will be tested in this class? How can I get a good grade? HW#1 due next Thursday

12. Survey to be answered by clickers 1.What is your background for light and color? Choose the one which best describes your science background a)I have had no physics in high school or college b)I have had physics in high school but not in college c)I have taken a physics course OR a psychology course at the college level d)I have taken more than one physics or psychology courses (high school and/or college level) e)I am a science major

13. Survey to be answered by clickers 2.Why did you take this course? Give the answer which best describes your reason. a)Because of requirements by the university b)Because it was recommended to me c)Because it looked easy d)Because it looked interesting e)I don't know why

14. Scientific notation and metric system Powers of 10 give a shorthand notation for very large numbers. 10 3 = 1000 10 2 = 100 10 1 = 10 10 0 = 1 Or very small numbers 10 -1 = 0.1 10 -2 = 0.01 10 -3 = 0.001 Scientists don't use feet or miles to indicate distances They use –meters (m) 1 meter = 39.4 inches –kilometers (km) 1 km = 1000 m = 0.625 mi –centimeters (cm) 1 cm = 10 -2 m = 0.394 inches –millimeters (mm) 1 mm = 10 -3 m –nanometers (nm) 1 nm = 10 -9 m

15. Clicker question What Lottery Prize you prefer? a)$ 10 3 b)$ 10 -8 c)$ 10 7 d)$ 10 0 e)$ 10 -18 wavelength = 500 nm = 5 x 10 2 x10 -9 m = 5 x 10 -7 m Hence 1 m = wavelength/(5 x 10 -7 ) = 10 7 /5 wavelengths = 2 million wavelengths Since 1 cm is 1/100 of a meter there are 2 x 10 6 /100 = 20,000 wavelengths in a cm

16. Clicker question The wavelength of green light is around 500 nm. How many wavelengths of green light fit into one cm (or a fingertip)? a)20 thousand b)50 thousand c) Two million d)Two billion e)5 billion 500 nm = 5 x 10 2 x10 -9 m = 5 x 10 -7 m 1 cm = 10 -2 m; Hence, 10 -2 /(5 x 10 -7 ) = 20,000 wavelengths in a cm

17. Intro and Chapter 1 Continued Light belongs to a family of waves called electromagnetic (EM) waves (Physics 2000) –Other waves: rope waves, water waves, sound waves, etc. Sometimes EM waves are called EM radiation –Radio waves –Radar and similar waves microwaves cell phone waves –Infrared or heat waves –Ultra-violet (suntan) waves –X-rays –Gamma rays EM waves are created and destroyed by emission and absorption –Classical picture (Phys 2000) wiggling electrons radiate radio waves or radar waves electrons in an atom are resonant with emitted or absorbed light waves or X-rays –Quantum picture (Phys 2000) change of state of electrons in atoms when bundles of wave energy (photons) are emitted or absorbed Light sources –Incandescent light bulb –Neon light –Fluorescent light

21. Rays (a single beam of light, for example) Single light ray –Ray from a laser acts like a single light ray –Illustrate by laser light through fog –Bounce off mirror –Bounce off white card –Put through water (bending) We only see light when a ray enters into our eye –Laser light is visible from side because it is scattered into our eyes Rays from a flashlight Rays from a light bulb What about light coming from everything in this room? Two kinds of objects: –Self luminous objects (lights) –Objects which are not self- luminous are seen because of light reflected off them Turn out the light and we don't see anything in the room It's all reflected light with many rays coming from diffuse surfaces

22. Laser Flashlight Light bulb Incident ray from a light bulb MANY reflected rays come from all parts of Alex, including his nose - a diffuse object Bob sees Alex's nose because a reflected light ray enters Bob's eye! Light rays are invisible unless they enter directly into our eye or are scattered by smoke, fog or some object into your eye!

23. Rays bounce when they reflect off a mirror or shiny surface Mirror This is called specular reflection. How is it different from diffuse reflection?

24. Rays bounce when they reflect off a mirror or shiny surface Mirror This is called specular reflection. How is it different from diffuse reflection?

25. http://phet.colorado.edu/sims/string-wave/string-wave_en.html

26. Waves Rope waves –Created by oscillation of my hand holding the rope –Finite speed of wave, but rope segments do NOT move in direction of wave –Rope segments move up and down, not along wave –Note the change that occurs when I oscillate my hand faster Radio wave transmitter –3 meters wavelength –(100 Mhz frequency) Google search under keyword "physics" –Water waves (circular pattern) –Stadium waves

36. Period and frequency of a wave and relation to wavelength and speed The period, T, is the time for the wave to make one complete cycle (say, top-bottom-top) AT ONE FIXED SPOT Think of my hand moving to make the rope wave. The period is the time for my hand holding the rope to make one complete top- bottom-top (or bottom-top-bottom) motion. The frequency, f, of the wave is equal to one over the period: f = 1/T f has the units of 1/secs, which we call Hertz (Hz) The frequency, f, is related to the speed of the wave, c and its wavelength, (lambda): f c

38. What would happen if sound waves could propagate through empty space???

47. We see color when waves of different wavelengths enter enter our eyes! Light with wavelength of 650 nm appears red when it enters a viewers eye Light with wavelength of 520 nm appears green when it enters a viewers eye Light with wavelength of 470 nm appears blue when it enters a viewers eye The speed of light in empty space is the same for all wavelengths

48. Clicker questions Which of the light waves has the longest wavelength? Which of the light waves is brightest? Which of the light waves has the highest speed in empty space? a)b) c) d)They all have the same speed a) b) c)

49. Clicker question What does Alex see when the wave at left with wavelength 650 nm goes by him? a)Red b)Blue c)Green d)White e)Nothing

50. What happens when two or more waves with different wavelengths reach your eye? Light with both wavelengths 650 nm and 520 nm appears yellow when it enters a viewers eye Light with only wavelength 580 nm ALSO appears yellow when it enters a viewers eye (A DEEPER YELLOW THAN FOR THE CASE ABOVE)

51. What is white light? Light which is a mixture of 650, 520 and 470 nm wavelengths (and possibly more wavelengths) appears WHITE when it reaches your eye No single wavelength (mono- chromatic) wave appears white when it reaches your eye!

52. Light at wavelengths which we see as colors are part of a wider family of electro- magnetic waves

53. It's a good idea to remember some rough wavelengths associated with colors Violet and blue are what we see when shorter wavelength visible rays enter our eyes. –They have relatively higher frequencies Red is how we see longer wavelength visible rays –Red has a relatively smaller frequency

54. What happens when those other electromagnetic waves enter our eyes? Wavelength = 10 million nm We don't see anything because electromagnetic waves at this frequency cannot excite a resonance in the atoms in our eyes. Note that this wavelength is on the order of a centimeter These are microwaves just like those sent out and received by your cellphones (or used in a microwave oven). We cannot see them even when they enter our eyes because their wavelength is too long to excite a resonance. Note that the frequency is f = c/   (3 x 10 8 m/s)/(10 -2 m) = 3 x 10 10 Hz

60. How much time it takes for the wave to travel distance of 9000 km? Speed of sound 340 m/s Speed of electromagnetic waves 300,000 km/s ;

61. How does an ordinary incandescent light bulb work? Electrode leading to one side of the wall plug Electrode leading to the other side of the wall plug Filament with current of electrons which hit into atoms causing light to be emitted Gas Atom Electrons Light emitted at many different resonance frequencies of atoms appears as white light Atom

62. Neon lights have atoms with resonances at special colors inside. They use alternating (AC) household current (Demo) Atom Electrons Neon light Atom

63. When rays come out in various different directions from an object or objects, the wavefront is defined as a curve or surface perpendicular to all the rays In this case the wavefront is expanding out spherically from the light bulb. Wherever it intersects a ray the wavefront is perpendicular to that ray –More technically, the tangent to the wavefront at the point of intersection is perpendicular to the ray The wavefront may be easier to visualize than the rays –You throw a pebble into a pond. The circularly expanding water waves are the wavefronts Light bulb Rays Wavefront

64. How are wave wiggles related to rays? Amplitude { Wavelength { Speed of light in empty space is c = 186,000 miles/sec = 3 x 10 8 meters/sec Ray Note, the wave is NOT "red." I have colored it red. We perceive it as red because of its wavelength. Waveform They are perpendicular rayray WigglesWiggles Light with a SINGLE wavelength is called monochromatic light Light with a SINGLE wavelength is called monochromatic light

65. HW #1 is due today