Chapter 10: Introduction to Waves

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• Chapter 10 Introduction to Waves Optics

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Lecture Outline

• Models of Light Rays Waves
• Reflection
• Refraction
• Total Internal Reflection
• Fiber Optics and Applications

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Model of Light Rays Waves

• Light characteristics
• Rectilinear propagation
• Light travels in straight lines
• Reflection
• When light is incident on a smooth surface it
  turns back into the original medium
• Refraction
• The path of light changes when it enters a
  transparent medium

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Properties of Light

• In vacuum light always travel at the same speed,
• Visible light is just one particular type of
  electromagnetic radiation. Other types of
  electromagnetic radiation include radio waves,
  infrared radiation (heat), ultraviolet radiation,
  x-rays and -rays. The different types of
  radiation are distinguished by their wavelength,
  or frequency

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The Electromagnetic Spectrum
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Properties of Wave
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Wavelength
Wave crest as seen from above
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Rays

• A ray is a line drawn from one wave crest to
  another which intersects each crest at right
  angles, as in figure. For light waves, the rays
  always point in the direction of the motion. Rays
  therefore provide a useful representation for
  describing the motion of light waves

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Reflection

• When light strikes the boundary between two
  media
• Some light incident on surface is reflected
• Some passes into the glass
• Partially absorbed
• Partially transmitted
• Transmitted light undergoes a change in
  direction, called refraction.

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Law of Reflection

• Two basic law of reflection
• The angle of incidence is equal to the angle of
  refraction.
• The incident ray, the reflected ray and the
  normal to the surface all lie in the same plane.
• Light reflection from a smooth surface is called
  regular or specular reflection.
• A rough or irregular surface will spread out and
  scatter the incident light resulting diffuse
  reflection

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Refraction

• Definition bending of a light ray as it passes
  obliquely from one medium to another.

?i angle of incidence ?r angle of refraction
?i
Air
Water
?r
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Index of Refraction

• Index of refraction, n of a particular material
  is the ratio of the free space velocity of light
  to the velocity of light through the material.
• Different value for different material (velocity
  of light in a material is different for different
  wavelength)
• Example nwater1.33, nglass1.50
• Unitless quantity and usually n gt 1

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Law of Refraction

• Two basic law of refraction
• The incident ray, the refracted ray and the
  normal to the surface all lie in the same plane.
• The path of a ray refracted at the interference
  between to media is exactly reversible.

N
?i
Air
Water
?r
N
?r
Air
Water
?i
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Fiber Optics Applications

• Larger bandwidth than copper wire
• gtinformation transmitted during fixed time period
• Increased information carrying capacity
• Based on the concept of total internal reflection
• Light passing through one medium encounters 2nd
  medium of lower optical density
• Fiber optic structure
• ncoregtncladding

Core
Buffer for protection
Cladding
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Fiber Optics Applications

• Advantages
• Immunity to electromagnetic interference
• Improved data security
• Higher transmission speed
• Increased signal bandwidth
• Applications
• Communication
• Sensors
• Medical instruments
• ???

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Fiber Optic Internal Reflection
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Fiber Optic Structure
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Fiber Optic Cables
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Summary Learning Outcomes

• Models of Light Rays Waves
• Describe the properties of light, waves and rays
• Reflection
• Define and illustrate the concept of reflection
• State the law of reflection
• Refraction
• Define index of refraction and state the law of
  refraction
• Apply Snells Law to solve problem involving
  transmission of light in two or more media.
• Determine change of velocity or wavelength of
  light as it moves in different media
• Total Internal Reflection
• Explain the concept of total internal reflection
  and the critical angle and use this idea to solve
  problems
• Fiber Optics and Applications
• Know how fiber optic work, its advantages and its
  applications.