Index of Refraction

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Index of Refraction

• The speed of light in any material is less than
  that in a vacuum (3 x 108 m/s)
• There is a continual absorption and re-emission
  of light by atoms in the material which slows
  down the lights passage
• v c/n where n is the index of refraction

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Refraction Snells Law

• Pass light from one medium to another

Some of the light will be reflected and some will
cross the boundary. The light that crosses is
bent. Think about a marching band moving into a
muddy field from a dry field.
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Refraction Snells Law
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Refraction Illusions
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Fiber Optics

• There is a critical angle going from high index
  to low index where the light is bent to 90o
• Past that angle, the light is reflected!!

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Fiber Optic Cable

• Lots of medical applications
• Colonoscopes, bronchoscopes, endoscopes
• Keyhole surgeries that are less invasive and heal
  faster

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Thin Lenses

• Parallel rays are brought to a focus
• Define a focal length like in mirrors
• Optometrists and ophthalmologists use Power P
  1/f where Diopter meter-1

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Thin Lenses

• Same game for diverging lenses with the focus on
  the opposite side of the lens from the converging
  lense case

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Lens Ray Tracing
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Lens Ray Tracing

• Same game with the same three rays but the image
  is upright and on same side of lens as the object

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The Lens Equation
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The Lens Equation
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Rules

• f is positive for converging, negative for
  diverging
• Object distance is positive if on side where
  light comes from
• Image distance positive if on opposite side of
  where light comes from
• Height of image is positive if upright and
  negative if inverted

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Magnifying Glass

• Place the object inside the focal point
• Image is virtual and larger

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Combinations of Lenses

• The image from the first lens is then the object
  for the second lens

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Lensmakers Equation
Thickness exaggerated to see things better.
Approximations
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Lensmakers Equation
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Lensmakers Equation
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Lensmakers Equation
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Lensmakers Equation