chapter 22 quiz - department of physics at uf · phy2054: chapter 22 10 chapter 22 quiz Îfor...

$: Chapter 22 Quiz - Department of Physics at UF · PHY2054: Chapter 22 10 Chapter 22 Quiz ÎFor refracted light rays, the angle of refraction: (a) is always equal to the incident angle$
PHY2054: Chapter 22 9

Chapter 22 QuizSnell’s Law describes:

(a) Huygens’ construction(b) Magnification(c) Reflection(d) Refraction


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


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=


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)Angular spreading (“dispersion”) of colors due to refraction


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)


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


Critical Angleθ < θc beam partly reflected & partly refracted at boundary

Rays 1, 2, 3

θ > θc beam is entirely reflected at the boundary (ray 5)Total internal reflection occurs only when n1 > n2

2 1sin /c n nθ =

90°


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 =


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


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


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


Construction of Fiber Optic Cable

Single mode fiber


Medical applicationsVisual scoping of internal organs, arteries, joints, etc.

Uses bundles of fibers to form an image


Fiber Optic Cables


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


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


National Lambda Rail Fiber Infrastructure

Only NLR Backbone links shown

www.nlr.net/


Florida Lambda Rail (10 Florida Universities)

www.flrnet.org/

chapter 22 quiz - department of physics at uf · phy2054: chapter 22 10 chapter 22 quiz Îfor...

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