Lenses

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Lenses

• Physics 40
• Chapter 2 -- Optics

2
Last Time

• Law of Reflection
• Images
• Curved Mirrors
• Question was She takes a photo of her friend
  Will she see?

3
This Time

• Refraction
• Lenses
• Optical Instruments

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Law of Refraction

• Ancient Greeks
• Light Bends
• Which Way, but not how much
• Wilebrod Snell
• Dutch astronomer
• In 1621 Discovered Sine Law

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Convex Lenses

• Bends Light toward Axis
• far from axis
• nearer
• Axis
• below Axis
• Point where they cross is Focal Point

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Focal Length

• Depends on how much the light bends
• Index of Refraction
• Water 1.33
• Fruit Juice 1.4
• Glass 1.5
• Diamond 2.41

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Real Images in Lenses

• Parallel to focal point
• Axis
• Focal point to Parallel

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The Lens Equation

• Same trick as with concave mirrors
• using refrcation triangles

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Virtual Images

• If object is closser than focal point
• Lens diverges light, but not enough to cross.
  Only diverges less

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Eye glasses

• Most people who need glasses are near sighted
• Lens thin in middle makes an image closer and
  smaller
• Smaller is unfortunate

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Telescopes

• Objective demagnifies, but produces a nice real
  image
• Eye piece is a magnifier.
• Trick is for the objective to be weak and the
  eyepiece strong.

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Microscopes

• Objective in a compound microscope magnifies
• Eyepiece magnifies an already magnified image

EYEPIECE
OBJECTIVE
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Next Time

• Question
• How do imaginary mirrors
• help a pool player
• Forces
• Same and opposite directions
• Perpendicular
• Any old direction