Announcements 11/10/10
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Prayer
Still missing slinkies from:
a. Stephen Grant
b. Jon Mortensen
c. Chris Read
d. Roger Brown
e. Tess Larson (She dropped the class; she’s just
on the list here so I don’t forget about her)
Another compound lens problem
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Class designed
Ray diagram = ?
q=?
Overall magnification = ?
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
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. The effective distance of the unmagnified image from
the eye is 25 cm for a magnifying glass and nearly
infinite for a telescope
e. It is likely to show up on an exam.
m = q/q0 … where q0 = “the best you can
do without magnification”
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
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. (This 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)
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?
“Colton picture” for q
Answers:
q = foh/(rfe)
q0 = h/r
m = fo/fe
These focal spots should essentially
overlap (not shown properly in this figure)
“Colton picture” for q
r
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.
Compound Microscope
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I really disliked the book’s somewhat arbitrary
“overall magnification” = Mobjective  meyepiece
(but apparently everyone does it that way)
Mobjective  -L/fo (ray diagram, object near focus of
objective, image near eyepiece)
meyepiece between
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mmax = 1 + 25cm/fe, and
mmin = 25cm/fe
Not on HW, not on exam, not especially
interesting…let’s not bother with any more.
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