Refraction

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Refraction
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Refraction
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Focal Point of a Thin Lens
Lens acts as a series of prisms
Focal point
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Add a lens to magnify the image
Keplerian Astronomical Telescope
Lens acts as a series of prisms
Focal point
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Properities of Lenses and a Refracting Telesope
Determining the focal length of a lens
1 1 1 f
do di
The focal length, f, of a lens is given by the
formula


di
distance from lens to the object distance from
the lens to the image
do
di
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Properities of Lenses and a Refracting Telesope
Determining the focal length of a lens
1 1 1 f
do di
What happens when the object is very, very far
away?


or f di
di
This is what we will verify in the first part of
the Lab!
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Properities of Lenses and a Refracting Telesope
Magnification of a Lens
di
hi
ho
hi
Magnification
ho
We will also verify this magnification equality
NOTE In our case the object is only the bulb!
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Properties of Lenses and a Refracting Telescope

• Lab Check List
• What is the focal length of your lens for an
  object at infinity,
• i.e. for an object very, very far away?
• Is the Data table for part 1 complete, readable
  and neat?
• - have you measured the distance to the image
  and
• the height of each image for the given
  distances to the object
• express the magnification hi/ho and di/do as
  decimal value!
• are the magnification values hi/ho and di/do
  close? 6
• What is happening to f as do gets larger?

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Properties of Lenses and a Refracting Telescope
Part 2 - Building a Telescope

• Lab Check List - Building the telescope.
• Magnification of the telescope can also be
  expressed as
• fobjective
• 
  f eyepiece
• Complete the table on page 72 -
• Enter the color of the lens and its focal
  length.
• How do we determine the focal length of a lens
  for an object
• very, very far away?
• Choose a lens for your telescopes eye piece and
• a lens for the objective lens
• Write why you chose the lens that you did next to
  the table.
• Build the telescope and view some objects
  outside.
• In question c
• what is the long focal length divided by the
  short focal length?

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For an object at infinity di large f
hi
do x di
Magnification
Formula for f
ho
do di