Snell s Law describes: (a) Huygens construction (b) Magnification (c) Reflection (d) Refraction Chapter 22 Quiz 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
Speed decreases Wavelength decreases Frequency constant Refractive index is variable Depends on λ n decreases as λ increases Dispersion When light travels from one medium to another: cn = c/ n λ = c / f = c/ n / f = λ / n n n n ( ) PHY2054: Chapter 22 11
n decreases as λ increases Dispersion For red light (λ = 700 nm) n is smaller (less bending) For blue light (λ = 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 c n = c / n PHY2054: Chapter 22 14
Critical Angle θ < θ c beam partly reflected & partly refracted at boundary Rays 1, 2, 3 θ > θ c beam is entirely reflected at the boundary (ray 5) Total internal reflection occurs only when n 1 > n 2 sin θ c = n / n 2 1 90 PHY2054: Chapter 22 15
Critical Angles (to vacuum) sinθ = 1/ c n Substance Vacuum Air Ice Water Ethyl Alcohol Glycerine Crown glass Sodium chloride Quartz Heavy flint glass Tooth enamel Sapphire Heaviest flint glass Diamond N Critical angle 1 90.0 1.00029 88.6 1.31 49.8 1.333 48.6 1.36 47.3 1.473 42.8 1.52 41.1 1.54 40.5 1.544 40.4 1.65 37.3 1.655 37.2 1.77 34.4 1.89 31.9 2.42 24.4 PHY2054: Chapter 22 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
Total internal reflection Chapter 22 Quiz (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
Total internal reflection Chapter 22 Quiz (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 www.nlr.net/ Only NLR Backbone links shown PHY2054: Chapter 22 26
Florida Lambda Rail (10 Florida Universities) www.flrnet.org/ PHY2054: Chapter 22 27