following reflected and refracted rays - university of florida · following reflected and refracted...
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PHY2054: Chapter 22 8
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 9
Chapter 22 QuizSnell’s Law describes:
(a) Huygens’ construction(b) Magnification(c) Reflection(d) Refraction
PHY2054: Chapter 22 10
Chapter 22 QuizFor 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 11
DispersionWhen light travels from one medium to another:
Speed decreasesWavelength decreasesFrequency constant
Refractive index is variableDepends on λn decreases as λ increases
nn
( )/ / / /n nc f c n f nλ λ= = =/nc c n=
PHY2054: Chapter 22 12
Dispersionn decreases as λ increases
For red light (λ = 700 nm) ⇒ n is smaller (less bending)For blue light (λ = 400 nm) ⇒ n is bigger (more bending)Spreading (“dispersion”) of colors due to refraction
PHY2054: Chapter 22 13
Rainbows Formed by DispersionLight 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 14
Understanding Refraction in Wave PictureConsider a row of soldiers slowing down in the mud
Wave fronts “turn” due to change of speed in the mediumAnalysis based on Huygens principleCloser analysis yields Snell’s law with cn = c / n
PHY2054: Chapter 22 15
Critical Angleθ < θc beam partly reflected & partly refracted at boundary
θ > θc beam is entirely reflected at the boundaryTotal internal reflection occurs only when n1 > n2
2 1sin /c n nθ =
90°
2 1sin /c n nθ =
PHY2054: Chapter 22 16
Critical Angles (to vacuum)
24.4°2.42Diamond31.9°1.89Heaviest flint glass34.4°1.77Sapphire37.2°1.655Tooth enamel37.3°1.65Heavy flint glass40.4°1.544Quartz40.5°1.54Sodium chloride41.1°1.52Crown glass42.8°1.473Glycerine47.3°1.36Ethyl Alcohol48.6°1.333Water49.8°1.31Ice88.6°1.00029Air90.0°1Vacuum
Critical angleNSubstance
sin 1/c nθ =
PHY2054: Chapter 22 17
Intensity During Transition to Critical AngleTransition is actually very smooth
Incident ray is reflected and refractedAs incident angle approaches critical angle, intensity of refracted ray goes to zero and reflected ray takes all the intensity
PHY2054: Chapter 22 18
Fiber OpticsBased on total internal reflection
Fiber has inner “core” of optically dense glassOuter “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 19
Fiber Optic ConstructionTrick is to make core absorb no light
So light can be transmitted over long distancesRequires ultra-pure glass (no impurities, variations)
Many fibers can be carried in a bundle
PHY2054: Chapter 22 21
Medical applicationsVisual scoping of internal organs, arteries, joints, etc.
Uses bundles of fibers to form an image
PHY2054: Chapter 22 23
Communications ApplicationsOptical 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 boostNot susceptible to electrical noise
Replacing copper wires for long distance communication
PHY2054: Chapter 22 24
Chapter 22 QuizTotal 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
www.nlr.net/