Announcements 3/18/11
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Prayer
Term project progress report due tomorrow night!
See website for details.
Exam 2 graded. Median = 90.5, medan = 83.0.
Still missing slinkies from a couple of you.
I’ll be out of town Mon & Wed of next week. Dr.
Peatross and Dr. Durfee will substitute
Regular office hours from now on (…except for
next week Mon & Wed, because I’ll be out of
town.)
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
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
because it mixes absolute magnification with
angular magnification
(but apparently everyone does it that way)
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Not on reading assignment, not on HW, not on
exam, not especially interesting… let’s not
bother with. Onward!
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
Interference...
Two sources
Double slit experiment
aka “Young’s Double Slit”
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Exactly the same as
the two speaker
demo
min
max
min
Goal: what’s the
shape of that curve?
How can we predict
where the maxima
& minima will be?
screen
here
intensity
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max