Reflection and refraction by HC120426013859

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




       Wrong Path
                                 True Path


                    MIRROR
   Law of Reflection
“The angle of incidence equals the
       angle of reflection.”

This is true for both flat mirrors and
            curved mirrors.
       Normal Line


A    Angle of       Angle of     B
    Incidence   =   Reflection




           MIRROR
                    Tangent
     Incidence
    Normal
       Reflection


C            F
       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)
    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.
        Mirror Images
A   B       C              D              E

                          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


A   B       C              D              E
Concave Mirrors
Light from Infinite Distance


                        Focuses at
                         the focal
    C        F             point
 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
C   F
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
C   F
C   F
C   F
        Virtual
        Image




C   F
Mirror Equations
C   F
Mirror Equation: do> C
f = 2 cm, C = 4 cm, ho = 2 cm, do = 5cm, di = ?
                1/f = 1/do + 1/di
                1/2 = 1/5 + 1/di
       1/di = 1/2 - 1/5 = 0.5 – 0.2 = 0.3
                 di = 3.33 cm
     M = hi/ho = -di/do  (-ho x di )/ do = hi
                hi = (-2 x 3.3)/5
                  hi = -1.3 cm
              M = - di / do = -0.66
C   F
C   F
Mirror Equation: C >do>f
 f = 2 cm, C = 4 cm, ho = 2 cm, do = 3 cm, di = ?
                  1/f = 1/do + 1/di
                  1/2 = 1/3 + 1/di
      1/di = 1/2 - 1/3 = 0.5 – 0.333 = 0.167
                    di = 6.0 cm
      M = hi/ho = -di/do  (-ho x di )/ do = hi
                   hi = (-2 x 6)/3
                      hi = -4.0
                M = - di / do = -2.0
C   F
C   F
Mirror Equation: do = f
f = 2 cm, C = 4 cm, ho = 2 cm, do = 2 cm, di = ?
                1/f = 1/do + 1/di
                1/2 = 1/2 + 1/di
        1/di = 1/2 - 1/2 = 0.5 – 0.5 = 0
               di =  no image
C   F
        Virtual
        Image




C   F
Mirror Equation: do < f
f = 2 cm, C = 4 cm, ho = 2 cm, do = 1 cm, di = ?
                1/f = 1/do + 1/di
                 1/2 = 1/1 + 1/di
       1/di = 1/2 - 1/1 = 0.5 – 1.0 = -0.5
                  di = -2.0 cm
     M = hi/ho = -di/do  (-ho x di )/ do = hi
                 hi = (-2 x -2)/1
                    hi = +4.0
               M = - di / do = 2.0
        Virtual
        Image




C   F
  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
                Real Image



    C       F




                   Virtual
                   Image

C       F
Will an image ever
 focus at a single
   point with a
 convex mirror?



          F

   Therefore, the
  images you see
    are virtual!
        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
Normal
Line




         Less Dense


         More Dense
 Light Beam          Normal
                     Line #1

              Fast



AIR


                               Slow
WATER




AIR
Normal
Line



         More Dense



         Less Dense
 Light Beam          Normal
                     Line #1

              Fast



AIR


                               Slow
WATER




AIR
                                         Fast

                               Normal
                               Line #2
       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.
http://cougar.slvhs.slv.k12.ca.us/~pboomer/physicslectures/secondsemester/light/refraction/refraction.html
           Refraction
Observer




 AIR

 WATER
                    False Fish



                    True Fish
Atmospheric Refraction

 Our atmosphere can
 bend light and create
distorted images called
        mirages.
Index of Refraction Equations
  • n = c/v = speed of light in a vacuum
               speed of light in medium
Index of Refraction Problem
 What is the speed of light in water, which has
 an index of refraction of 1.33?

 n = c/v  v = c/n

 v = (2.998 x 108 m/s) / 1.33

 V = 2.25 x 108 m/s
Index of Refraction Equations
  • n = c/v = speed of light in a vacuum
              speed of light in medium

  • n = sin i/sin r
Index of Refraction Problem
 A ray of light enters a piece of crown glass at
 an angle of 57o and is refracted to 31o inside
 the glass. What is the index of refraction?
 n = sin i/sin r
   = sin 57o / sin 31o
   = 1.63
Index of Refraction Equations
  • n = c/v = speed of light in a vacuum
              speed of light in medium
  • n = sin i/sin r

  • sin A / sin B = nB / nA
Index of Refraction Problem
  A diamond (n = 2.42) is in water (n = 1.33)
  and a ray of light shines on it making an
  angle of incidence of 55o. What is the
  angle of refraction inside the diamond?

  sin A / sin B = nB / nA

  sin 55o / sin B = 2.42/1.33

  B = 27o
                   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.
Diverging or
Concave Lens




    C          F   F   C
            Converging or
            Convex Lens




C   F   F          C
Converging or
Convex Lens
Converging or
Convex Lens




    C       F   F   C
            Converging
            or Convex
               Lens




C   F   F       C
 Lens Equation: do> C
f = 2 cm, C = 4 cm, ho = 2 cm, do = 5cm, di = ?
                1/f = 1/do + 1/di
                1/2 = 1/5 + 1/di
       1/di = 1/2 - 1/5 = 0.5 – 0.2 = 0.3
                 di = 3.33 cm
     M = hi/ho = -di/do  (-ho x di )/ do = hi
                hi = (-2 x 3.3)/5
                  hi = -1.3 cm
            Converging
            or Convex
               Lens




C   F   F       C
            Converging
            or Convex
               Lens




C   F   F       C
            Converging
            or Convex
               Lens




C   F   F       C
            Converging
            or Convex
               Lens




C   F   F       C
            Converging
            or Convex
               Lens




C   F   F      C
Mirror Equation: do < f
f = 2 cm, C = 4 cm, ho = 2 cm, do = 0.5 cm, di = ?
                 1/f = 1/do + 1/di
                  1/2 = 1/1 + 1/di
       1/di = 1/2 - 1/0.5 = 0.5 – 2.0 = -1.5
                    di = -.67 cm
      M = hi/ho = -di/do  (-ho x di )/ do = hi
                hi = (-2 x -.67)/0.5
                hi = +8/3 = +3.67
               M = - di / do = +1.33
            Converging
            or Convex
               Lens




C   F   F      C
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
http://cougar.slvhs.slv.k12.ca.us/~pboomer/physicslectures/secondsemester/light/refraction/refraction.html
Air – Water Interface
           sin θ = n2/n1
Air nair = 1 and Water n2 = 1.33
   sin θ = 1.00/1.33 = 0.750
           sin θ = 0.750
          θ = sin-1 0.750
              θ = 49o
                 Refraction




Critical Angle                        AIR

                                    WATER
                              49


  Total                            Light
 Internal                          Source
Reflection
  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
Fiber Has More Capacity

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

                     Fiber Optics Association
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
    Why Use Fiber Optics?
•   Economics
•   Speed
•   Distance
•   Weight/size
•   Freedom from interference
•   Electrical isolation
•   Security
                        Fiber Optics Association
  Fiber Optic Applications
• Fiber is already used in:
  – > 90% of all long distance telephony
  – > 50% of all local telephony
  – Most CATV networks
  – Most LAN (computer network)
    backbones
  – Many video surveillance links

                           Fiber Optics Association
  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
Fiber Technology




          Fiber Optics Association
Fiber Technology




          Fiber Optics Association
Fiber Optic Data Links
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
 Wavelength-Division Multiplexing




Fiber Optics Association
        Fiber Optic Cable

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



                        Fiber Optics Association
   Fiber Optic Connectors
• Terminates the fibers
• Connects to other fibers or
  transmission equipment
    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
 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
              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
Air – Diamond Interface
             sin 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
http://cougar.slvhs.slv.k12.ca.us/~pboomer/physicslectures/secondsemester/light/refraction/refraction.html
          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
                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!
           Polarization
• Unpolarized light has random directions of
  the electric field vector
• Light can be polarized by:
   – (1) passing light though a polarizer
     material or
   – (2) reflecting light off of a solid or liquid
     surface.
• For example, reflected light from a lake is
  mostly horizontally polarized.
 Polarization of Light Waves



• Each atom produces a wave with
  its own orientation of E
• All directions of the electric field
  vector are equally possible and lie
  in a plane perpendicular to the
  direction of propagation
• This is an unpolarized wave          General Physics
 Polarization of Light, cont
• A wave is said to be linearly
  polarized if the resultant electric
  field vibrates in the same
  direction at all times at a
  particular point
• Polarization can be obtained
  from an unpolarized beam by
   – Selective absorption
   – Reflection
   – Scattering
                                  General Physics
Polarization by Selective Absorption
  • E. H. Land discovered a material that
    polarizes light through selective
    absorption
     – He called the material Polaroid
     – The molecules readily absorb light
       whose electric field vector is parallel
       to their lengths and transmit light
       whose electric field vector is
       perpendicular to their lengths
                              General Physics
   Selective Absorption, cont




• The most common technique for polarizing light
• Uses a material that transmits waves whose electric field
  vectors in the plane are parallel to a certain direction and
  absorbs waves whose electric field vectors are
  perpendicular to that direction
                                       General Physics
    Polarization by Reflection
• When an unpolarized light beam is reflected from a
  surface, the reflected light is
  – Completely polarized
  – Partially polarized
  – Unpolarized
• It depends on the angle of incidence
  – If the angle is 0° or 90°, the reflected beam is
    unpolarized
  – For angles between this, there is some degree of
    polarization
  – For one particular angle, the beam is completely
    polarized                          General Physics
   Polarization by Reflection, cont
• The angle of incidence for
  which the reflected beam
  is completely polarized is
  called the polarizing
  angle, θp
• Brewster’s Law relates the
  polarizing angle to the
  index of refraction for the
  material
                                 sin p
• θp may also be called       n          tan p
  Brewster’s Angle               cos  p

                                 General Physics

								
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