Title: Refraction
1Refraction
2Refraction
3Focal Point of a Thin Lens
Lens acts as a series of prisms
Focal point
4Add a lens to magnify the image
Keplerian Astronomical Telescope
Lens acts as a series of prisms
Focal point
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7Properities 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
8Properities 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!
9Properities 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!
10Properties 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?
11Properties 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?
12 For an object at infinity di large f
hi
do x di
Magnification
Formula for f
ho
do di