Rainbows

1
Lecture 5

• Rainbows
• Prisms
• Note Please read section 5.5 of Hecht prior to
  your lab session

2
Sir Isaac Newton

• English Physicist (1643-1727)
• Liked to play with light
• link

3
Rainbows
Rainbows are beautiful
4
Rainbows
Some are really awesome !!!!
link
5
Rainbows
Some dont even need rain !!!!
link
6
Rainbows
How do they form? The French Philosopher Rene
Descartes (link) Explained the phenomenon Arc-en-
Ciel (link) By considering how light reflects
and refracts in water droplets
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Rainbows

• Light enters into water droplet
• At air water interface the light is refracted
• At the rear of the water droplet the light is
  reflected
• As light exits it is refracted once more
• Dispersion separates the white light into the
  RAINBOW of colors nred1.333 nviolet1.346
• Applet
• derivation

8
Rainbows
Observer must be positioned properly to observe
the rainbow
9
Prisms

• Transparent bodies (glass sapphire,)with plane
  faces
• Change direction of light by refraction and
  reflection.
• Important Function is to deviate
• Light of different colors into different
  directions.
• DISPERSION dn/dl
• Another Function is to reorient images

• Prism applet

10
Uses of prisms

• Binoculars link
• Telescopes link
• Spectroscopes link

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Prism Spectrometer
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Types of Prisms (link)

• Dispersing
• Triangular
• Pellin-Broca
• Abbe
• Reflective
• Porro
• Dove
• Amici Roof
• Penta
• Polarizing

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Triangular Prism

• Deviates and disperses light

14
Pellin-Broca Prism

• Constant deviation dispersing prism
• Used to select single wavelengths by rotating
  about point O
• Useful for Spectroscopy
• link

15
Abbe Prism

• Another constant dispersing prism
• link

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Reflecting Prisms

• Not Dispersive ? Achromatic
• Internal Reflection
• Sometimes silvered faces

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Porro Prism

• Right angle prism
• Oriented to deviate light by 180 degrees
• link

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Dove Prism

• Truncated version of right angle prism
• Rotates image
• link

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Amici Roof Prism

• Truncated right angle prism
• Splits image down the middle, interchanges left
  and right
• Used in telescopes to correct for reversion due
  to lenses
• link

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Penta Prism

• The Penta Prism will deviate the beam by 90 deg
  without affecting the orientation of the image

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Deviation Angle of Triangle Prism

• Link
• link2

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Deviation Angle of Triangle Prism
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Minimum Deviation Angle

• For minimum deviation, ray traverses prism
  symmetrically
• qi1qt2