Transcript Slide 1
Light passing from a medium in which it is ________ slow faster to one in which it is __________________ : q2 fast slow refracted reflected q1 increase Now _______________q 1: q2 fast slow q1 less refracted more reflected q2 equals 900 Keep increasing q1 until_______________________. critical At that point, q1 is called the _________________angle, qc. q2 = 900 fast slow q1= qc > qc For any angle q1 ______: fast even less refracted even more reflected no refracted slow q1> qc all light is reflected Total Internal Reflection (TIR). This is called________________________________________ It can only occur when light passes into a medium in which it is faster ____________________________ . To find qc: q2 = 900 n2 = fast n1 = slow Snell’s Law: qc n1sinq1 = n2sinq2 n1sinqc = n2sin900 If fast medium is air: n1sinqc = 1·1 sinqc = 1/n1 qc = sin-1(1/n1) Here are some typical critical angles for slow media with air as the fast medium: slow medium n1 1/n1 qc water 1.33 0.752 490 Lucite 1.50 0.667 420 diamond 2.42 0.413 240 A beam of light enters Lucite: no refracted ray here q1 > 420 Totally internally reflected ray Lucite with a ray at less than the critical angle: incident ray q1 < 420 refracted ray here internally reflected ray, but not total Of what use is TIR? Fiber optics. Why fiber optics instead of electrical wire? attenuation 1. Less _______________________(dying out) of signal… “repeaters” 2. …means less ____________________are needed more info 3. Light has a high f ___________________can be sent 4. Each fiber can carry __________________because >1 signal > 1 frequency _____________________ (color) can be sent on one fiber. 5. More signals per wire ____________________needed less wires interference 6. Light is immune to electrical __________________ environmental noise from other fibers and_______________________________ explosive fumes 7. Can be used where _____________________are present Fiber Optics: Manufacture: 1. Can be made of plastic or glass. 2. Glass has less attenuation, so it is used for longer distances. Uses: 1 transmitting information on cable 2. sensors for seismic, sonar and oil drilling 3. optical gyroscopes in planes and cars 4. illumination in medicine and decoration Gyroscopes are used to stabilize ships, airplanes, and satellites. Toy: On a ship: Optical gyroscopes: Rotation causes the light going around in one direction to have a shorter path. Using mirrors: Using fiber optics: The red and blue dots represent photons going around a fiber optic path in different directions. Other uses of TIR… binoculars: periscopes: prisms mirrors Ex: Underwater, you can only see a 970 “cone” of light above you that represents the entire sky. 970 All light incident on the surface from below within the blue area is totally reflected back into the water. This is called "Snell's Window." What keeps polar bears warm? 1. Their fur traps air. 2. The fur hairs act like fiber optic light pipes that channel UV down to their skin. 3. Guess what color their skin is! Warning….next photo shows … In a vacuum, all frequencies (colors) of light travel ______________________. This is ____________in any at the speed c false other media. Why? slower more 1. Higher f ___________interactions _____________ 2. natural Higher f closer to ________________f of molecules resonance slower more ___________________________ Media in which the speed of a wave depends on its dispersive frequency ___________________ are said to be______________________. wave non-dispersive medium dispersive media sound air liquids and solids light vacuum gases, liquids and solids The Dark Side of the dispersion of light: ROYGBIV the visible spectrum Dispersion separation _______________________is the ____________________of a frequencies wave into its different _______________________. incident white light Notice: The rays leaving the block are parallel because the block sides are parallel. glass block blue red it changes v more Blue bends ___________ because_________________________ more higher Blue has a ___________________ index of refraction. a glass prism Dispersion with _____________________: red incident white light blue Note: the rays are NOT parallel to the incident ray because the sides of the glass prism are not parallel more Blue bends ______________ going in, more and it bends ________________ coming out. Newton's Experiment: white light board with hole prism 2nd prism Before Newton: White light is “pure.” The prism “stained” the white light. After Newton: White light contains all colors. Herschel’s (musician, astronomer, physicist) did the following experiment: ~1800 temp. of thermometer B Y R Why did the temp. keep increasing beyond red? Rainbows are caused by dispersion. 1. incident white 2. some reflected 3. 1st refraction 4. dispersion 5. total internal reflection 6. 2nd refraction 7. rainbow For details about how the raindrop does it, press here. Why the arc? What time of day is best for rainbows? Sometimes, a double rainbow is seen: Why is the secondary rainbow fainter??? A lens is basically _________________ two prisms separated by a rectangular block: lens focus for blue light ______ white light white light focus for red light ______ Not all colors focus _____________________ at the same point . This is called___________________________________ chromatic (color) aberration. Newton did not think that lenses could be cured of chromatic aberration. So he invented a telescope that the Law of Reflection. was based on__________________________ All colors incident at the same spot will reflect the same angle: with _______________________ parabolic mirror white light focus no aberration All colors focus at the same spot __________________. Later, the achromatic doublet was discovered: two lenses with different indices of refraction that mostly corrects for chromatic aberration. The first achromatic refracting lens was invented in 1733 by an English barrister named Chester Moore Hall although it was independently invented and patented by John Dollond. What makes diamonds so beautiful? Diamonds are optically “dense.” high amount of dispersion color small critical angle light trapped fire