How well do you know Lenses?

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How well do you know Lenses?

• Lenses work because of
• A. refraction B. reflection c. Both

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Lenses refract light!

• Converging Lenses (a) are thicker in the middle
  Diverging Lenses (b) are thinner

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How are mirrors like Lenses?

• A concave lens acts much likea. concave
  mirror b. convex mirrorc. flat mirror d. convex
  lens

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1. refract not reflect2. behave opposite of
mirrors(concave mirror convex lens)3. assume
thin so easy geometry4. brighter than
mirrors(no light loss to absorption)5. less
perfect than mirrors(lens sensitive to color
angle)
Lenses
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Lens Aberrations
Spherical chromatic
Astigmatism
Coma
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Lens Terminology
The Center of Curvature is equal to the radius of
the circle formed by the lens
focus
Principal Axis
C
f
Center of Curvature
vertex
Note f C/2
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which lens is converging?A. top-focuses b.
bottom-defocuses
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Sign Conventions for Lenses
Focal length f for convex, f - for concave
f 5 cm
f -5 cm
Object distance do for objects on left
side Image distance di for real images on
left side -
for virtual images on right side
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• Converging and Diverging Lenses
• 3 Principle Rays

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a positive lens (f) is also calleda.
converging b. convex c. diverging d. concave
e. both a b f. both c d
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Negative Lens (f-) also called concave or
diverging
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Convex LensesPrincipal Ray1(parallel, then
opposite focal point)
C
f
C
f
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Practice Ray Tracing!
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Convex Lens Principal Ray2(from focus,
through lens parallel)
C
f
C
f
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Practice Ray Tracing!
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Convex LensPrincipal Ray3(no change through
lens middle)
C
f
C
f
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Practice Ray Tracing!
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• 3 unique locations to place at object
• 1. further than focal point (d gt f)
• 2. At focal point (df)
• 3. Less than focal point (d lt f)

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• What is the magnification of an object placed at
  the center of a convex lens?
• a. 1 b. 2 c. -1 d. -2 e. 0

Magnification -1 (same size, but inverted.
Real too!)
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• What type of image comes from placing an object
  far from a convex lens?A. real, inverted B.
  real, upright
• C. virtual, upright D. virtual, inverted

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• What type of image comes from placing an object
  far from a convex lens?A. real, inverted B.
  real, upright
• C. virtual, upright D. virtual, inverted

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• What happens to the image as the object (candle)
  is placed closer to the lens?A. bigger B.
  smaller C. same

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• Which case for placing an object would create a
  real image?A. 1 B. 2 C. 1, 2, 3 d. 4

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Concave Lens Principal Ray1(parallel, diverge
as if from focal point
f
f
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Concave Lens Principal Ray2(aim for far focal
point, hit lens, then emerge parallel out)
f
f
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Concave Lens Principal Ray3(no changed through
middle of lens)
f
f
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What type image do concave lenses (convex
mirrors) always make?A. real, small B.
virtual, bigC. real, big D. virtual, small
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Which lens can produce a virtual, upright, large
image?A. concave b. convex c. both d. neither
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Which lens can produce a real, upright, large
image?A. concave b. convex c. both d. neither
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How can you create a real, inverted, large
image?A. concave- object between f and lensB.
concave- object between f and 2f (C) C. concave-
object past the center (C)D. convex- object
placed anywhere
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FYI Multiple Lenses

• The real image of one lens becomes the object for
  the next image!Why need to know this?
• compound lenses are found in cameras,
  telescopes,

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FYI Camera

• Lens sold based on lowest f-numberI Intensity
  is 4x stronger if f-number is 2x as low(price
  4x higher too!)

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FYI The Eye

• The camera is modeled after the eye
• Normal reading distance is 25 cm
• Eye is about 2.5 cm in diameter
• Most of focusing is done by the cornea and
  vitreous humor behind the cornea

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Myopia near sighted (cant see far)

• Contacts diverges light so not so focused

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Hyperopia far sighted(cant see near)

• Reading glasses- convex lens adds focus

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FYI Telescopes astronomical is most
powerful, but stars upside down !

• Astronomical Telescope-
• 2 converging lenses (objective, eyepiece)
• Image is inverted, virtual, magnified

• Terrestial (Galilean Telescope)-
• 1 converging lens 1 diverging lens
• Image is upright, virtual, magnified

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Astronomical Telescope

• Note the image from the objective lens is
  inverted
• The image is inside the focal point of the
  eyepiece (for magnification)

Object
Eye
fo
fo
Image
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Astronomical Telescope

• The image from the objective lens is treated as
  an object for the eyepiece
• Note that since it is inside the focal point of
  the eyepiece the final image is magnified

Eye
fo
fo
Final Image
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Terrestrial Telescope

• Note that the eyepiece is located inside the
  focal point of the objective lens
• The diverging eyepiece lens intercepts the rays
  of light from the objective lens before the image
  can be inverted magnifies the final image

Eye
fe
fe
fo
fo
Eyepiece
Objective Lens
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FYI Astronomical Telescope

• Object is at infinity so image is at f
• Measure angular magnification
• Length of telescope light path is sum of focal
  lengths of objective and eyepiece

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FYI Compound Microscope

• Magnification is product of lateral magnification
  of objective and angular magnification of
  eyepiece
• Note Image is viewed at infinity

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Compound Microscope

• Note that the compound micrscope is similar to an
  astronomical telescope backwards
• The objective lens forms a real, enlarged,
  inverted image inside the focal point of the
  eyepiece

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Compound Microscope

• The objective lens forms a real, enlarged,
  inverted image inside the focal point of the
  eyepiece
• The first image is further magnified by the
  eyepiece--thus the term compound

Object
fe
fo
fo
Final Magnified Image