PHY2049ch33%284-02-10%29 - Chapter 21 Quiz Which of the...

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Unformatted text preview: Chapter 21 Quiz Which of the following has nothing to do with EM waves? (a) Dental x-rays (b) Radio broadcasting (c) Strumming a guitar (d) Cooking a microwave dinner (e) Responding with your HITT transmitter PHY2054: Chapter 22 1 Chapter 21 Quiz A grain of interplanetary dust is in the Sun’s gravitational field. Ignoring all other influences, is it possible for the grain to move away from the Sun? (a) Yes, if the grain is sufficiently large (b) Yes, if the grain is sufficiently small (c) No, it cannot escape the Sun’s gravitational field PHY2054: Chapter 22 2 Chapter 21 Quiz Which statement is true? The energy carried by an electromagnetic wave in a vacuum (a) propagates at the speed of light (b) consists of only electric field contributions (c) propagates along the direction of the electric field (d) consists of E and B fields pointing in the same direction (e) none of the above PHY2054: Chapter 22 3 Chapter 22: Reflection Law of reflection Incident ray, reflected ray, normal lie in one plane PHY2054: Chapter 22 4 Reflection Law Applies to non-Flat Surfaces PHY2054: Chapter 22 5 Chapter 22: Refraction Index of refraction n and speed of light in medium Law of refraction (Snell’s law) Incident ray, refracted ray, normal lie in one plane n1 n2 PHY2054: Chapter 22 6 Refraction at Air-Water Interface 1 2 0° 15° 30° 45° 60° 75° 90° 0° 11.2° 22.0° 32.0° 40.5° 46.4° 48.6° Critical angle (more later) PHY2054: Chapter 22 7 Following Reflected and Refracted Rays Ray 1 is the incident ray Ray 2 is the reflected ray Ray 3 is refracted into the lucite Ray 4 is reflected in the lucite Ray 5 is refracted as it enters the air from the lucite PHY2054: Chapter 22 8 Chapter 22 Quiz Snell’s Law describes: (a) Huygens’ construction (b) Magnification (c) Reflection (d) Refraction PHY2054: Chapter 22 9 Chapter 22 Quiz For refracted light rays, the angle of refraction: (a) is always equal to the incident angle (b) is always greater than the incident angle (c) is always less than the incident angle (d) is always equal to the critical angle (e) can be less than, greater than, or equal to angle of incidence PHY2054: Chapter 22 10 Dispersion When light travels from one medium to another: Speed decreases Wavelength decreases Frequency constant Refractive index is variable n decreases as increases PHY2054: Chapter 22 11 Dispersion n decreases as increases For red light ( = 700 nm) n is smaller (less bending) For blue light ( = 400 nm) n is bigger (more bending) Angular spreading (“dispersion”) of colors due to refraction PHY2054: Chapter 22 12 Rainbows Formed by Dispersion Light is refracted by spherical water droplets Sun must be behind you (rainbow is circular, with sun on axis) Red light bent at a lesser angle (top of rainbow) Violet light bent at a greater angle (bottom of rainbow) PHY2054: Chapter 22 13 Understanding Refraction in Wave Picture Consider a row of soldiers slowing down in the mud Wave fronts “turn” due to change of speed in the medium Analysis based on Huygens principle Closer analysis yields Snell’s law with cn = c / n PHY2054: Chapter 22 14 Critical Angle < > c beam partly reflected & partly refracted at boundary beam is entirely reflected at the boundary (ray 5) Rays 1, 2, 3 Total internal reflection occurs only when n1 > n2 c 90° PHY2054: Chapter 22 15 Critical Angles (to vacuum) Substance Vacuum Air Ice Water Ethyl Alcohol Glycerine Crown glass Sodium chloride Quartz Heavy flint glass Tooth enamel Sapphire Heaviest flint glass Diamond N 1 1.00029 1.31 1.333 1.36 1.473 1.52 1.54 1.544 1.65 1.655 1.77 1.89 2.42 PHY2054: Chapter 22 Critical angle 90.0° 88.6° 49.8° 48.6° 47.3° 42.8° 41.1° 40.5° 40.4° 37.3° 37.2° 34.4° 31.9° 24.4° 16 Intensity During Transition to Critical Angle Transition is actually very smooth Incident ray is reflected and refracted As incident angle approaches critical angle, intensity of refracted ray goes to zero and reflected ray takes all the intensity PHY2054: Chapter 22 17 Fiber Optics Based on total internal reflection Fiber has inner “core” of optically dense glass Outer “cladding” of less optically dense glass Light rays passed through core to make shallow reflections with surface 100% reflection at each bounce PHY2054: Chapter 22 18 Fiber Optic Construction Trick is to make core absorb no light So light can be transmitted over long distances Requires ultra-pure glass (no impurities, variations) Many fibers can be carried in a bundle PHY2054: Chapter 22 19 Construction of Fiber Optic Cable Single mode fiber PHY2054: Chapter 22 20 Medical applications Visual scoping of internal organs, arteries, joints, etc. Uses bundles of fibers to form an image PHY2054: Chapter 22 21 Fiber Optic Cables PHY2054: Chapter 22 22 Communications Applications Optical fibers can carry digital information Telephone, networks, Internet High frequency of light high rate of information transfer “High bandwidth”, several Tb/s over single fiber Signals can travel ~ 100 km before needing boost Not susceptible to electrical noise Replacing copper wires for long distance communication PHY2054: Chapter 22 23 Chapter 22 Quiz Total internal reflection (a) refers to light being reflected from a plane mirror (b) may occur when a fisherman looks at a fish in a lake (c) may occur when a fish looks at a fisherman on a lake PHY2054: Chapter 22 24 Chapter 22 Quiz Total internal reflection (a) refers to light being reflected from a plane mirror (b) may occur when a fisherman looks at a fish in a lake (c) may occur when a fish looks at a fisherman on a lake PHY2054: Chapter 22 25 National Lambda Rail Fiber Infrastructure Only NLR Backbone links shown PHY2054: Chapter 22 26 Florida Lambda Rail (12 Florida Universities) PHY2054: Chapter 22 27 ...
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This note was uploaded on 05/17/2011 for the course PHY 2049 taught by Professor Any during the Spring '08 term at University of Florida.

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