LENSES

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• LENSES

Lyzinski Physics
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Light Speeds

• When traveling through a vacuum, light travels at
  3 x 108 m/s. This is the fastest light ever
  travels. We shall refer to this as the SPEED OF
  LIGHT.
• When traveling through a different medium
  (substance), light slows down.
• The INDEX OF REFRACTION compares this slower
  speed to the speed of light in a vacuum.

Speed of light
Speed of light in new medium
Index of refraction
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The Index of Refraction

• What does refract mean. It means to bend.
  When light travels from one medium to another it
  actually bends (thus causing it to either slow
  down or speed up)
• The index of refraction is always GREATER THAN 1
  (because the speed in a medium is always less
  than the speed of light).
• Optically DENSE mediums have a higher index.
  We will call these mediums HEAVY
• Optically LESS DENSE mediums will be called
  LITE (mis-spelled ?)

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Some common mediums
Medium Index of Refraction
vacuum 1.00
air 1.003
water 1.33
ethanol 1.36
fluorite 1.43
crown glass 1.52
quartz 1.54
Zircon 1.92
diamond 2.42
More Dense
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Refraction (the bending of light)
Normal to the surface
Normal to the surface
Crown glass
n 1.52
air
n 1.00
water
water
n 1.33
n 1.33
If light travels from HEAVY into LITE, it bends
AWAY FROM the normal
If light goes from LITE to HEAVY, it bends TOWARD
the normal.
La-Hite (LHT)
Ha-La (HLA)
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Total Internal Reflection
Ha-La has a Phenomena associated with it.
Normal
heavy
lite
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SNELLS LAW
How much does the light bend???
Relates the angles to the indexes
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Prisms cause light to bend
LHT
HLA
IMPORTANT QUESTION Does all light bend the same
amount?
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All light does NOT bend the same amount in a
prism.
Why does the index increase going from R to I (in
ROY-G-BIV)?
Increasing index (bend) Decreasing wavelength
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The Wave Equation
The frequency of light never changes once it is
created. Velocity can change. Wavelength will
then also change. But frequency never changes
once the wave is generated.
If v goes , then l must go . If v goes , n
goes .
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Refraction (the bending of light)
Normal to the surface
H
L
If light travels from HEAVY into LITE, it speeds
up AND the wavelength increases
If light goes from LITE to HEAVY, it slows down
AND the wavelength decreases.
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Concave Lenses
Concave lenses are similar to stacking two prisms.
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Convex Lenses
Convex lenses are also similar to stacking two
prisms.
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How do you locate the image formed in a LENSE
Situation.

1. Any ray parallel to the principal axis is
   reflected through the focus.

2. Any ray through the focus is reflected
parallel to the principal axis.
3. Any ray through the center of the lens passes
directly through the lense following its same
path.
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Image Formation in CONVERGING Lenses
Same Size, Inverted, Real
NO IMAGE!!!
VIRTUAL!!!
Smaller, Inverted, Real
LARGER, Inverted, Real
F 2F
2F F
Inside F
Outside 2F
On 2F
Between 2F F
On F
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Image Formation in Diverging Lenses
F
F
All images are VIRTUAL and smaller than the object
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Cameras
BOTH use converging lenses with the object far
beyond the secondary focus.
Film
.. and the human eye
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Magnifying Glasses
F 2F
2F F
Larger, virtual image that you see
Object that you are looking at (under the lens)
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Film Projectors
White screen
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Microscopes
Lens 2 (Eyepiece)
Lens 1 (Objective)
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The Human Eye
Cornea Protective Window of
eye Iris Colored part that acts like a
camera shutter. Pupil Hole in the middle of
the iris. Lens has adjustable
focal length. Retina Where image is
formed. Optic nerve Sends image to
brain where it is flipped upside down.
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Near-Sightedness
Diverging Lens creates a virtual image of the
far away object that is inside (or at) the far
point. The eye sees this virtual image clearly.
Object beyond the far point cant be focused
clearly on the retina ? Fuzzy vision
Furthest Point that the eye can see clearly
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Far-Sightedness
Object inside the near point cant be focused
clearly on the retina ? Fuzzy vision
Closest Point that the eye can see clearly