Order Of Magnitude Estimation

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Results of Exam 3
Average78
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Physics 202, Lecture 25

• Todays Topics
• Lenses
• Reminder
• Cameras
• The Human Eye, Lenses and Magnifiers
• Combination of Lenses
• Microscopes
• Telescopes

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Ray Diagrams

• If image can be formed, only two rays are
  necessary to determine an image point.
• Useful rays
• Object ray pointing to the center (C)
• ? image ray inline with the object ray
• Object ray parallel to principal axis
• ?image ray pointing to a focal point (F)
• Object ray passing through a focal point
• ? image ray parallel to principal axix.

optical device
O
principal axis
F
F
C
I
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Image Formation Equation and Magnification
Parameters p object distance q image
distance h object height h image height M
magnification f focal length
Mirrors and Thin Lenses
If Mlt1 ? Image lt Object If Mgt1 ? Image gt
Object If Mlt0 ? Image ?? Object If Mgt0 ? Image ??
Object
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Sign Conventions
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Cameras

• A cameras is essentially a converging lens with a
  short focal length. (Operating condition pgtgtf ?
  q f)

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Eyes

• Eye is essentially an auto-focus camera

Psychological size (image size on retinal) is
determined by q
Quick quiz Is the image on retina real/virtual,
upright/inverted?
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Simple Magnifier

• A simple magnifier is essentially also a
  converging lens with a short focal length.
• Operating condition pltf and q-25 cm
• Simple magnifiers magnify the opening angle an
  object subtends at the eye (i.e. psychological
  size)

angular magnification m q/q0 25cm/f for
near point
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Combination of Lenses
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Compound Microscopes (cont)
Robert Hookes Microscope (1665)
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Compound Microscopes

• Compound microscope also does angular
  magnification.
• Configuration L gtgt fefo

MoL/fo Me25 cm/fe MMoMe (L/fo) (25 cm/fe)
Final Image Virtual, inverted
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Telescopes (cont)
Galileos Telescope
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Telescopes

• Telescope is another type of angular
  magnification device with configuration L fefo

Note For telescope application, object distance
can not be adjusted.
Mo fo/fe