Physics 1230 light and color ivan i smalyukh, instructor

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, PM - PM Grading Assistants: Jian Yao, Yiheng Lin, Hao Song Lectures Homeworks Exams Hands-on experience Demonstrations Peer Instruction (with extra credit) Fun Course Business • Website Website http://www.colorado.edu/physics/phys1230/ http://www.colorado.edu/physics/phys1230/phys1230_fa09/ phys1230_fa09/ • Syllabus Syllabus – Science Science of of light light and and color color – HW HW assignments, assignments, reading reading and and exam exam dates dates • Course Course info info – Grades Grades – Clicker Clicker technology technology • Another Another kind kind of of invisible invisible wave wave 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? Ornithoptera chimaera chimaera Ornithoptera priamus urvillianus Ornithoptera goliath supremus, f titan Papilio blumei blumei What will be tested in this class? How can I get a good grade? Ability to: Memorize "Understand" new Deeper understanding: Be able to new facts concepts at a figure out new things using concepts and minimal level definitions Percent of grade: 25% 25% 50% (only 15% uses math) HW#1 due next Thursday 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 (monochromatic) wave appears white when it reaches your eye! Light at wavelengths which we see as colors are part of a wider family of electromagnetic 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 What happens when those other electromagnetic waves enter our eyes? Wavelength = 10 million nm Note that the frequency is f = c/λ =(3 x 108 m/s)/(10-2 m) = x 1010 Hz • 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 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 ; How does an ordinary incandescent light bulb work? Filament with current of electrons which hit into atoms causing light to be emitted Gas Atom Atom Electrons Electrode leading to the other side of the wall plug Atom Light emitted at many different resonance frequencies of atoms appears as white light Electrode leading to one side of the wall plug Neon lights have atoms with resonances at special colors inside They use alternating (AC) household current (Demo) Atom Atom Electrons Atom Neon light 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 Wavefront Rays Light bulb • 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 How are wave wiggles related to rays? Light with a SINGLE wavelength is called monochromatic light They They are are perpendicular perpendicular Amplitude { Wiggles Speed of light in empty space is c = 186,000 miles/sec = x 108 meters/sec Wavelength { ray Ray Waveform Note, the wave is NOT "red." I have colored it red We perceive it as red because of its wavelength HW #1 is due today [...]... light 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 •... light bulb • What about light coming from everything in this room? Two kinds of objects: – Self luminous objects (lights) – Objects which are not selfluminous 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 Light rays are invisible unless they enter directly into our eye or are... 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... 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. .. or some object into your eye! Laser Flashlight Light bulb MANY reflected rays come from all parts of Alex, including his nose - a diffuse object Incident ray from a light bulb Bob sees Alex's nose because a reflected light ray enters Bob's eye! Rays bounce when they reflect off a mirror or shiny surface • This is called specular reflection • How is it different from diffuse reflection? Mirror Rays bounce... level) e) I am a science major 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 Scientific notation and metric system • Powers of 10 give a shorthand notation for very large numbers... bounce when they reflect off a mirror or shiny surface • This is called specular reflection • How is it different from diffuse reflection? Mirror http://phet.colorado.edu/sims/string-wave/string-wave_en.html 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 –... 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 • The wavelength of green light is around 500 nm How many wavelengths of green light fit into one cm (or a fingertip)? a) b) c) d) e) 20 thousand 50 thousand Two million Two billion 5 billion • 500 nm = 5 x 102 x10-9 m = 5 x 10-7 m • 1... wavelengths in a cm 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. .. 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 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