PHY138

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PHY138 Waves, Lecture 8Todays overview

• Total Internal Reflection
• Optical Fibres
• Images Formed by Flat Mirrors

Real Laser Shining Through a Cloud
Real Laser
Laser as seen on TV and movies
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Reading Assignment

• Please read the following from Serway and Jewett
  before class on Monday Chapter 26, Sections 26.4
  - 26.6 and Context 7 Conclusion on page 1037.
• A www.masteringphysics.com assignment is due this
  Friday at 500 PM. It is the last Mastering
  Physics assignment of the semester.
• (hoot.)

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air
water
A fish swims below the surface of the water. An
observer sees the fish at 1. a greater depth
than it really is. 2. its true depth. 3. a
smaller depth than it really is.
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Notes from last lecture

• The index of refraction, n, of air depends on
  temperature n decreases as air Temperature
  increases
• When a ray enters a layer of different n, it
  bends
• If n decreases, the ray bends away from the
  normal. This is refraction.
• Refraction effects cause mirages, twinkling of
  starlight, and heat currents off hot highways
  or other surfaces.

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Hot air near the ground
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Temperature Inversion Hot air above
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Total Internal Reflection

• Occurs when n2ltn1
• ?c critical angle.
• When ?1 ?c, no light is transmitted through the
  boundary 100 reflection

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An Optical Fibre
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Quiz 2
mirror
O
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3
An observer O, facing a mirror, observes a light
source S. Where does O perceive the mirror image
of S to be located? (5 none of the points
shown.)
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S
2
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Virtual Image in a flat mirror

• Light rays emerging from an object obey the law
  of reflection for the specular surface of a
  mirror
• Our mind imagines that the rays emerge from
  points beyond the mirror.
• This thing beyond the mirror is called an image.
  No light rays actually pass through the image, so
  it is virtual.
• It is convenient to describe the size and
  location of the image as if it were an actual
  thing.

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How an image is formed