Announcements 11/9/11
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Prayer
Term project progress report due Saturday night
a. Evidence of progress
b. Text in body of email, who is in your group, CC
group members
Slinkies! (Thomas, Mike, Rachael, this means
you)
Frank & Ernest
(with apologies
to Pluto)
Thought question
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Which will look bigger* to you, a 1 m tall object
that’s 5 meters away from you, or a 10 m tall
image that’s 50 meters away from you?
a. 1 m tall object
b. 10 m tall image
c. same
*
In the sense that it takes up more of your field of view
“angular size”
Worked Problem
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What is the angular size of a 0.1 m tall object
that’s 5 meters away from you?
Two methods!
Thought Question
 Which method should you use?
a. Method A
b. Method B
Quick writing
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You are looking at an ant, h = 1 mm. What
is the maximum viewing angle you can use
to look at the ant, without any lenses?
“Colton picture”
r
q
q (in radians) = (section of arc)/r
Reading Quiz
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Which of the following is NOT true of angular magnification?
a. It is more useful than the absolute magnification when
discussing telescopes
b. It is more useful than the abs. magnification when
discussing magnifying glasses
c. It is given by the equation m = -q/p
d. It is likely to show up on an exam.
m = q/q0 … where q0 = “the best you can
do without magnification”
Magnifying Glass
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The setup:
f = 10 cm
Where would you like the image to be?
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Let’s pick q = -50 cm. (q would generally be given in
problem.)
Answers:
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What is m? (m = q/q0)
q = 6h/50 rad
a. What is q?
q0 = h/25 rad
b. What is q0?
m=3
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Note: using formulas from book…
mmax = 3.5 (for q = 25 cm)
mmin = 2.5 (for q = infinity)
Aside: What will the ant see?
f = 10 cm
h
8.33 cm
If p = 1 cm:
q = (1/10 – 1/1)-1 = -1.11
M = -q/p = 1.11
1.11h 9.44
 1.10
h 9.33
m = q/q0 =
If p = 9.5 cm: q = (1/10 – 1/9.5)-1 = -190
(fixed from in- M = -q/p = 190/9.5 = 20
class values)
20h (190  8.33)
m = q/q0 = h (9.5  8.33)  1.80
p
If p = 20 cm: q =+20
(ant can’t see you!)
Quick writing
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You are looking at the planet Mars, “h”
(diameter, really) = 3.4  106 m. The planet,
as you are looking at it, is 2.5  1011 m away
(this changes from month to month based on
the relative positions of Mars and Earth).
What is the maximum viewing angle you can
use to look at Mars, without any lenses?
“Colton picture”
r
q
q (in radians) = (section of arc)/r
Telescope
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The setup:
Given details of
setup, what is m?
(m = q/q0)
a. What is q0?
b. What is q?
These focal spots should essentially
overlap (not shown properly in this figure)
“Colton picture” for q
r
Answers:
q0 = h/r
q = foh/(rfe)
m = fo/fe
fo
Because Mars is so far away, image is
formed at the focal spot (essentially)
Height of image = hfo/r
fe
(from M = -q/p)
triangle: q (rad) =
(intermed. height)/fe
q
image
If intermediate image were formed exactly at the
focal point of the eyepiece, final image would be
at . As it is, it will just be very far away.
Regardless of how far away it is, though,
the angle is given by the blue ray.
Reflecting Telescope
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A “Newtonian Reflector”
eyepiece lens
Incoming
Light
Curved
Mirror
Mirror
http://lcogt.net/en/book/reflecting-telescopes
Compound Microscope
I really dislike the eqn:
“overall magnification” =
Mobjective  meyepiece
because it mixes absolute
magnification with angular
magnification
(but apparently everyone does it
that way)
 Not on reading assignment, not
on HW, not on exam, not especially
interesting… let’s not bother with.
Onward!
http://en.wikipedia.org/wiki/Microscope
Chapter 37!
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Interference effects
a. I.e. now returning to wave nature of light,
instead of the ray approximation
Two mathematical facts we will use:
e e
cos x 
2
ix
ix
e e
sin x 
2i
ix
ix
Interference...
A single source
Next few slides: credit Dr. Durfee
Interference...
Two sources