Reflection%20and%20Refraction

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• Reflection and Refraction

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Reflection

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

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Principle 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

Wrong Path
True Path
MIRROR
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Law of Reflection

• The angle of incidence equals the angle of
  reflection.
• This is true for both flat mirrors and curved
  mirrors.

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MIRROR
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Types 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)

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Locating the Image for Plane Mirrors

1. Draw the image the same distance behind the
   mirror as the object is in front.
2. Draw a connector line from each object to each
   image.
3. If the connector line passes through the mirror,
   the image will be seen.

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These lines are pointed to the only images that
will be seen from each of the original locations
(A-E) NOTE No images will be seen from E
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Concave Mirrors


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Light from Infinite Distance
Focuses at the focal point

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Two Rules for Locating the Image 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

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Two Rules 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

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

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Virtual Image
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Real vs. Virtual Image

• When a real 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
  image location
• it only appears to an observer as though the
  light was emanating from the virtual image
  location

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Will an image ever focus at a single point with a
convex mirror?
Therefore, the images you see are virtual!
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Refraction

• Refraction 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

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Light Beam
AIR
WATER
AIR
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Light Beam
AIR
WATER
AIR
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Refraction 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.

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lectures/secondsemester/light/refraction/refractio
n.html
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Refraction
Observer
AIR
WATER
False Fish
True Fish
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Atmospheric Refraction

• Our atmosphere can bend light and create
  distorted images called mirages.

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Lenses

• 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.

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Diverging or Concave Lens
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Converging or Convex Lens
C
F
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Converging or Convex Lens
C
F
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Converging or Convex Lens
C
F
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Converging or Convex Lens
C
F
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Converging or Convex Lens
C
F
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Converging or Convex Lens
C
F
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Converging or Convex Lens
C
F
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Converging or Convex Lens
C
F
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Converging or Convex Lens
C
F
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Converging or Convex Lens
C
F
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Total Internal Reflection...

• is the total reflection of light traveling in a
  medium when it strikes a surface of a less dense
  medium
• sin ? n2/n1

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lectures/secondsemester/light/refraction/refractio
n.html
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Refraction
Critical Angle
AIR
WATER
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Total Internal Reflection
Light Source
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What Is Fiber Optics ?

• Transmitting communications signals over hair
  thin strands of glass or plastic
• Not a "new" technology
• Concept a century old
• Used commercially for last 25 years

Fiber Optics Association
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Fiber Has More Capacity

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

Fiber Optics Association
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Fiber Optic Communications

• Applications include
• Telephones
• Internet
• LANs - local area networks
• CATV - for video, voice and Internet connections
• Utilities - management of power grid
• Security - closed-circuit TV and intrusion
  sensors
• Military - everywhere!

Fiber Optics Association
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Why Use Fiber Optics?

• Economics
• Speed
• Distance
• Weight/size
• Freedom from interference
• Electrical isolation
• Security

Fiber Optics Association
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Fiber Optic Applications

• Fiber is already used in
• gt 90 of all long distance telephony
• gt 50 of all local telephony
• Most CATV networks
• Most LAN (computer network) backbones
• Many video surveillance links

Fiber Optics Association
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Fiber Optic Applications

• Fiber is the least expensive, most reliable
  method for high speed and/or long distance
  communications
• While we already transmit signals at Gigabits per
  second speeds, we have only started to utilize
  the potential bandwidth of fiber

Fiber Optics Association
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Fiber Technology
Fiber Optics Association
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Fiber Technology
Fiber Optics Association
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Fiber Optic Data Links
Fiber Optics Association
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Light Used In Fiber Optics

• Fiber optic systems transmit using infrared
  light, invisible to the human eye, because it
  goes further in the optical fiber at those
  wavelengths.

Fiber Optics Association
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Wavelength-Division Multiplexing
Fiber Optics Association
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Fiber Optic Cable

• Protects the fibers wherever they are installed
• May have 1 to over 1000 fibers

Fiber Optics Association
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Fiber Optic Connectors

• Terminates the fibers
• Connects to other fibers or transmission
  equipment

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Medical 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

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Fiberscope Construction

• 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

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Endoscopes

• 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

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Air Diamond Interface

• sin ? n2/n1
• Air nair 1 and Diamond n2 2.42
• sin ? 1.00/2.42 0.413
• sin ? 0.413
• ? sin-1 0.413
• ? 24o

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lectures/secondsemester/light/refraction/refractio
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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
• CDs
• Raindrops

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Rainbows

• 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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