Reflection and Refraction. Reflection Most objects we see reflect light rather than emit their own light

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Reflection and Reflection and RefractionRefraction

ReflectionReflection

Most objects we see reflect light rather than emit their own light.

Principle of Least TimePrinciple of Least Time• Fermat's principle - light travels in straight

lines and will take the path of least time to strike mirror and reflect from point A to B

MIRROR

A B

Wrong Path

True Path

Law of ReflectionLaw of Reflection

“The angle of incidence equals the angle of reflection.”

This is true for both flat mirrors and curved mirrors.

MIRROR

A BAngle of Angle of IncidenceIncidence

Angle of Angle of ReflectionReflection

Normal LineNormal Line

==

C F

Normal

Tangent

Incidence

Reflection

Types of ReflectionTypes of Reflection

Specular Reflection - images seen on smooth surfaces (e.g. plane mirrors)

Diffuse Reflection - diffuse light coming from a rough surface (cannot see a reflection of yourself)


Locating the Image for Locating the Image for Plane MirrorsPlane Mirrors

1.1. Draw the image the same distance behind Draw the image the same distance behind the mirror as the object is in front.the mirror as the object is in front.

2.2. Draw a connector line from each object to Draw a connector line from each object to each image.each image.

3.3. If the connector line passes through the If the connector line passes through the mirror, the image will be seen. mirror, the image will be seen.

A C D EBA EDB CMirror ImagesMirror Images

These lines are These lines are pointed to the only pointed to the only images that will be images that will be seen from each of seen from each of

the original the original locations (A-E) locations (A-E)

NOTENOTE: No : No images will be images will be

seen from Eseen from E


Concave MirrorsConcave Mirrors

Light from Infinite DistanceLight from Infinite Distance

C F

Focuses at the focal

point

Two Rules for Locating the Two Rules for Locating the Image for Concave MirrorsImage for Concave Mirrors

• Any incident ray traveling parallel to the principal axis on the way to the mirror will pass through the focal point upon reflection

C F

Two Rules for Concave MirrorsTwo Rules for Concave Mirrors

• Any incident ray passing through the focal point on the way to the mirror will travel parallel to the principal axis upon reflection

• Any incident ray traveling parallel to the principal axis on the way to the mirror will pass through the focal point upon reflection

C F

C F

C F

C F

Virtual Image

Real vs. Virtual ImageReal vs. Virtual Image• When a real imagereal image is formed, it still

appears to an observer as though light is diverging from the real image location– only in the case of a real image, light is

actually passing through the image location

• Light does not actually pass through the virtual imagevirtual image location– it only appears to an observer as though the

light was emanating from the virtual image location

C F

Real ImageReal Image

C F

Virtual Virtual ImageImage

F

Will an image Will an image ever focus at a ever focus at a

single point with a single point with a convex mirror?convex mirror?

Therefore, the images you see

are virtual!

RefractionRefractionRefraction is the bending of light

when it passes from one transparent medium to another

This bending is caused by differences in the speed of light in

the media

NormalNormalLineLine

More Dense

Less Dense

WATERWATER

AIRAIR

Normal Normal Line #1Line #1

SlowSlow

FastFast

Light BeamLight Beam

AIRAIR

NormalNormalLineLine

More Dense

Less Dense

WATERWATER

AIRAIR


SlowSlow

FastFast

Light BeamLight Beam

FastFastAIRAIR


Refraction ExamplesRefraction Examples

• Light slows down when it goes from air into water and bends toward the normal.

• An Analogy: A car slows down when it goes from pavement onto gravel and turns toward the normal.

• An Illusion : Fish in the water appear closer and nearer the surface.

http://cougar.slvhs.slv.k12.ca.us/~pboomer/physicslectures/secondsemester/light/refraction/refraction.html

RefractionRefraction

WATER

AIR

Observer

True Fish

False Fish

Atmospheric RefractionAtmospheric Refraction

Our atmosphere can bend light and create

distorted images called mirages.




LensesLenses• Work due to change of direction of light due to

refraction• Diverging Lens

• A lens that is thinner in the middle than at the edges, causing parallel light rays to diverge.

• Converging Lens• A lens that is thicker in the middle and

refracts parallel light rays passing through to a focus.

C F CF

Diverging or Diverging or Concave LensConcave Lens

C F CF

Converging or Converging or Convex LensConvex Lens

F F


C F CF


C F CF

Converging Converging or Convex or Convex

LensLens

C F CF


LensLens

C F CF


LensLens

C F CF


LensLens

C F CF


LensLens

C F CF


LensLens

C F CF


LensLens


Total Internal Reflection...Total Internal Reflection...

…is the total reflection of light traveling in a medium when it strikes

a surface of a less dense medium

sin θ = n2/n1


WATER

AIR

Light Light SourceSource

Critical AngleCritical Angle

Total Total Internal Internal

ReflectionReflection

RefractionRefraction

49




What Is Fiber Optics ? What Is Fiber Optics ? • Transmitting Transmitting

communications signals communications signals over hair thin strands over hair thin strands of glass or plasticof glass or plastic

• Not a "new" technology Not a "new" technology

• Concept a century oldConcept a century old• Used commercially for Used commercially for

last 25 yearslast 25 years

Fiber Optics Association

Fiber Has More CapacityFiber Has More Capacity

This single fiber This single fiber can carry more can carry more communications communications than the giant than the giant copper cable!copper cable!


Fiber Optic CommunicationsFiber Optic Communications• Applications include Applications include

– TelephonesTelephones– InternetInternet– LANs - local area networksLANs - local area networks– CATV - for video, voice and Internet CATV - for video, voice and Internet

connectionsconnections– Utilities - management of power gridUtilities - management of power grid– Security - closed-circuit TV and intrusion Security - closed-circuit TV and intrusion

sensorssensors– Military - everywhere!Military - everywhere!


Why Use Fiber Optics?Why Use Fiber Optics?• EconomicsEconomics

• SpeedSpeed

• DistanceDistance

• Weight/sizeWeight/size

• Freedom from interferenceFreedom from interference

• Electrical isolationElectrical isolation

• SecuritySecurityFiber Optics Association

Fiber Optic ApplicationsFiber Optic Applications• Fiber is already used in:Fiber is already used in:

– > 90% of all long distance telephony> 90% of all long distance telephony

– > 50% of all local telephony> 50% of all local telephony

– Most CATV networksMost CATV networks

– Most LAN (computer network) Most LAN (computer network) backbonesbackbones

– Many video surveillance linksMany video surveillance links


Fiber Optic ApplicationsFiber Optic Applications• Fiber is the least expensive, most Fiber is the least expensive, most

reliable method for high speed and/or reliable method for high speed and/or long distance communicationslong distance communications

• While we already transmit signals at While we already transmit signals at Gigabits per second speeds, we have Gigabits per second speeds, we have only started to utilize the potential only started to utilize the potential bandwidth of fiberbandwidth of fiber


Fiber TechnologyFiber Technology


Fiber TechnologyFiber Technology


Fiber Optic Data LinksFiber Optic Data Links

Light Used In Fiber OpticsLight Used In Fiber OpticsFiber optic systems transmit using Fiber optic systems transmit using

infrared light, invisible to the human infrared light, invisible to the human eye, because it goes further in the eye, because it goes further in the optical fiber at those wavelengths.optical fiber at those wavelengths.


Wavelength-Division MultiplexingWavelength-Division Multiplexing


Fiber Optic CableFiber Optic Cable

• Protects the fibers Protects the fibers wherever they are wherever they are installedinstalled

• May have 1 to over May have 1 to over 1000 fibers1000 fibers


Fiber Optic ConnectorsFiber Optic Connectors• Terminates the fibersTerminates the fibers

• Connects to other fibers or Connects to other fibers or transmission equipmenttransmission equipment

Medical FiberscopesMedical Fiberscopes• Electromagnetic radiation has played

a role in medicine for decades

• Particularly interesting is the ability to gain information without invasive procedures

• Using fiber optics in medicine has opened up new uses for lasers

Fiberscope Fiberscope ConstructionConstruction

• Fiberscopes were the first use of optical fibers in medicine

• Invented in 1957• The objective lens forms a real image on the end of the

bundle of fiber optics• This image is carried to the other end of the bundle

where an eyepiece is used to magnify the image

EndoscopesEndoscopes• An endoscope is a fiberscope with

additional channels besides those for illuminating and viewing fibers

• The uses of these extra channels may include– Introducing or withdrawing fluids– Vacuum suction– Scalpels for cutter or lasers for surgical

applications


Air – Diamond InterfaceAir – Diamond Interfacesin θ = n2/n1

Air nair = 1 and Diamond n2 = 2.42

sin θ = 1.00/2.42 = 0.413

sin θ = 0.413

θ = sin-1 0.413

θ = 24o


Dispersion...Dispersion...• …is the separation of white light into pure

colors (ROY G. BIV).

• The index of refraction is higher for higher frequencies, so violet is bent the most

• Dispersion Examples:

• Prisms

• Diffraction Gratings

• CD’s

• Raindrops



RainbowsRainbows

• Raindrops refract, reflect and disperse sunlight.

• Rainbows will always appear opposite of the Sun in the sky.

• You cannot run from or run to a rainbow!



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Reflection and Refraction. Reflection Most objects we see reflect light rather than emit their own light