Physics 1230: Light and Color Ivan I. Smalyukh, Instructor

1. 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 Physics 1230: LightandColorIvan I. Smalyukh, Instructor • Lectures • Homeworks • Exams • Hands-on experience • Demonstrations • Peer Instruction (with extra credit) • Fun

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

3. 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? Physics 1230: LightandColorIvan I. Smalyukh

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

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

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

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

13. Powers of 10 give a shorthand notation for very large numbers. 103 = 1000 102 = 100 101 = 10 100 = 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 Scientific notation and metric system

14. What Lottery Prize you prefer? $ 103 $ 10-8 $ 107 $ 100 $ 10-18 wavelength = 500 nm = 5 x 102 x10-9 m = 5 x 10-7 m Hence 1 m = wavelength/(5 x 10-7) = 107/5 wavelengths =2 million wavelengths Since 1 cm is 1/100 of a meter there are 2 x 106/100 = 20,000 wavelengths in a cm Clicker question

15. The wavelength of green light is around 500 nm. How many wavelengths of green light fit into one cm (or a fingertip)? 20 thousand 50 thousand Two million Two billion 5 billion 500 nm = 5 x 102 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 Clicker question

16. 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 Intro and Chapter 1 Continued

20. 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 Rays(a single beam of light, for example)

21. Light rays are invisible unless they enter directly into our eye or are scattered bysmoke, fog or some object into your eye! Seeing everything in terms of rays Laser MANY reflected rays comefrom all parts of Alex, includinghis nose - a diffuse object Flashlight Light bulb Incident ray from a light bulb Bob sees Alex's nose because a reflected light ray enters Bob's eye!

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

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

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

25. 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 Waves

35. 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 • 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): 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. f  = c

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

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

47. 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? b) c) They all have the same speed Clicker questions a) b) c)

48. What does Alex see when the wave at left with wavelength 650 nm goes by him? Red Blue Green White Nothing Clicker question

49. What happens when two or more waves with different wavelengths reach your eye? Light with both wavelengths 650 nm and520 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 YELLOWTHAN FOR THE CASE ABOVE)

50. 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) waveappears white when it reaches your eye!