Unformatted text preview: Physics 212
Lecture 28
Optical Devices Physics 212 Lecture 28, Slide 1 Music
Who is the Artist?
A)
B)
C)
D)
E) BB Ray Charles
Solomon Burke
Henry Butler
Johnny Adams
Otis Redding
“Rediscovered” Soul singer from 60’s
Absolutely Beautiful Voice Sad note: He passed this semester (Oct) Highly Recommended DVD:
“One Night History of the Blues” Theme of the week: Incredible singers
note: Solomon’s final album produced
final
by longtime Al Green producer
by
Physics 212 Lecture 28, Slide 2 Your Comments
“Are there any definite rules to determine
Are
when an image is real or virtual?”
when Real: s’ > 0
Virtual: s’ < 0 “Can we talk about this whole "far point" and "near
Can
point" stuff? It was a bit confusing. I am excited
to learn why my eyes are so incredibly awful and
how my contacts and glasses actually fix them.”
how We will do a brief summary LENGTHY
LENGTHY
DEMO / CALCULATION
DEMO
to finish lecture “EXPLAIN IN DETAIL AND VERY VERY
EXPLAIN
VERY
SLOWLY HOW TO DO THESE TWO
SLOWLY
LENS SYSTEMS... “
“I was hoping to discuss Faraday's Lae
was
Lae
because this is the first time i've ever
because
i've ever
heard of this. You haven't taught it in
class, so ill be pretty annoyed if its on
the final. I think this is a must to
review if it will be making its grand
appearance.”
appearance. I got a lot of these..
05 40
30
20
10
0 Confused Confident Physics 212 Lecture 28, Slide 3 How to Get a Comment Posted:
A Physics Joke I have not had my comments posted in either PHYS 211 or 212 and this is
have
my last physics class I need to take ( I am a biologist). Before discussing
my
discussing
what I want to see in lecture I would like to give a farewell joke. My
what
ke.
favorite physics joke which has gotten me through alot of tough times...
alot of
So you have a bunch of famous physicists visiting U of I and they decide
So
decide
to play a little game of tag in the parking lot of ISR (it's close to Loomis).
to
se
They establish there will be no tag backs and decide that Pascal will be
They
will
"it" first and they begin running. Well, Pascal runs up to Einstein and tags
"it"
ein
him first. So Einstein is looking around to see whom he will tag. While this
him
While
is going on, Newton is in the corner of the parking lot and he pulls a piece
is
ulls
of chalk out of his pocket and begins drawing a square around himself one
of
mself
meter on each side. Einstein, having seen this, thinks he will be an easy
meter
an
target so he runs up, tags Newton, and yells "You're it!". But Newton just
target
ewton
looks at him,smiles, and says "No tags backs!... I'm a Newton over a meter
him,smiles and
squared and that's a Pascal".
I would like additional examples of the near sighted and far sighted
would
hted
glasses. It would be helpful to have an understanding of the "weights"
glasses.
ights"
that each concept will have on the final exam even though many topics
that
opics
build off of one another. Thank you.
build
Physics 212 Lecture 28, Slide 4 Executive Summary – Mirrors & Lenses:
Executive
S > 2f
2f real
inverted
smaller 2f > S > f real
inverted
bigger f >S>0 f>0
concave virtual
upright
bigger (converging) converging f f S′
M =−
S 111
+=
S S′ f
f<0 S >0 virtual
upright
smaller convex
(diverging) diverging
f f Physics 212 Lecture 28, Slide 5 It’s always the same:
111
+=
S S′ f S′
M =−
S You just have to keep the signs straight:
s’ is positive for a real image
f is positive when it can produce a real image Lens sign conventions S:
S’ :
f: positive if object is “upstream” of lens
positive
of
positive if image is “downstream” of lens
positive
positive if converging lens
Mirrors sign conventions S:
S’ :
f: positive if object is “upstream” of mirror
positive
of
positive if image is “upstream” of mirror
positive
positive if converging mirror (concave)
Physics 212 Lecture 28, Slide 6 System of Lenses
• Trace rays through lenses, beginning with most upstream lens Image from first lens
Becomes object for second lens Physics 212 Lecture 28, Slide 7 System of Lenses
• Virtual Objects are Possible !! Object Distance is Negative !! Image from first lens
Becomes object for second lens Physics 212 Lecture 28, Slide 8 Normal Eye Physics 212 Lecture 28, Slide 9 Farsighted Converging Lens creates virtual image at person’s near point
Physics 212 Lecture 28, Slide 10
10 Nearsighted Fix with diverging lens that creates virtual image at far point.
Physics 212 Lecture 28, Slide 11
11 Preflight 2
BB A
B Farsighted = Converging Lens
Only Converging Lens can produce a
Only
REAL IMAGE !!
REAL 70
60
50
40
30
20
10
0 Physics 212 Lecture 28, Slide 12
12 Preflight 4
BB A
B
C 60
50
40
30
20
10
0 θr
θi d d The image is formed an equal distance BEHIND the mirror
Therefore, if you stand a distance = ½ of your near point,
Therefore,
of
the distance to the image will be the near point distance.
the Physics 212 Lecture 28, Slide 13
13 Preflight 6
BB A
B
C
D
E 1. Parallel rays are transmitted and pass
Parallel
through focal point (f1)
through
2. Those rays also pass through focal point of
Those
second lens (f2) and therefore are
second
and
transmitted parallel to the axis.
transmitted
3. f2 > f1 implies that the width > w1 25
20
15
10
5
0 Physics 212 Lecture 28, Slide 14
14 The Large Synoptic Survey Telescope Physics 212 Lecture 28, Slide 15
15 How to make a big telescope mirror
Melt it & spin it 52,000 lbs of borosilicate glass when filled
Physics 212 Lecture 28, Slide 16
16 Multiple Lenses Exercises
Two converging lenses are set up as shown. The focal length of each lens is 47
cm. The object is a light bulb located 70 cm in front of the first lens. s1=70 cm
f=47 cm BB What is the nature of the image from the first lens alone?
(A) REAL
UPRIGHT (B) REAL
INVERTED s>f
M =− s′ = s’ > 0
s′
s M<0 (D) VIRTUAL
INVERTED PICTURES EQUATIONS
111
=−
s′ f s (C) VIRTUAL
UPRIGHT fs
s− f Draw Rays as above real image
inverted image
Physics 212 Lecture 28, Slide 17
17 Multiple Lenses Exercises
Two converging lenses are set up as shown. The focal length of each lens is 47
cm. The object is a light bulb located 70 cm in front of the first lens.
Lens separation = 2 m
s1 = 70 cm
70
f = 47 cm
s1’ = 1.43 m What is the object distance s2 for lens 2?
(A) s2 = 1.43 m (B) s2 = +1.43 m (C) s2 = 0.57 m BB (D) s2 = +0.57 m (E) s2 = +2.7 m THE OBJECT FOR THE SECOND LENS
IS THE IMAGE OF THE FIRST LENS s2 = 0.57
OR
s2 = +0.57 Image of first lens is a REAL
Image
object for the second lens
object Physics 212 Lecture 28, Slide 18
18 Multiple Lenses Exercises
Two converging lenses are set up as shown. The focal length of each lens is 47
cm. The object is a light bulb located 70 cm in front of the first lens.
Lens separation = 2 m s1=70 cm
f=47 cm s1’ = 1.43 m
s2 = 0.57 m BB What is the nature of the FINAL image in terms of the ORIGINAL object?
(A) REAL
UPRIGHT (B) REAL
INVERTED fs2
s2 − f s2 > f
M2 = − s2′
s2 (D) VIRTUAL
INVERTED PICTURES EQUATIONS
s2′ = (C) VIRTUAL
UPRIGHT Draw Rays as above
s2’ > 0 real image RESULTS
s2’ = 2.69 m M2 < 0 M = M1M2 > 0 M = 9.6 upright image
Physics 212 Lecture 28, Slide 19
19 Multiple Lenses Exercises
Suppose we increase the initial object distance to 74 cm
BB Lens separation = 2 m s1=74 cm
f=47 cm RESULTS
s1’ : 1.43 m Ø 1.29 m
1.43 How does the L, the distance to the FINAL image, change?
(A) L increases (B) L decreases s2’ : 2.69 m Ø 1.38 m
2.69 (C) L remains the same Step through images, one at a time
WORDS
Increasing s1 will decrease s1’
(moving closer to focal point would
(moving
increase the image distance)
Decreasing s1’ will increase s2
Increasing s2 will decrease s2’ EQUATIONS
111
=−
s1′ f s1 s2 = 2m − s1′
111
=−
s2′ f s2 1
increases
s1′ s2 increases
1
increases
s2′ Physics 212 Lecture 28, Slide 20
20 Multiple Lenses Exercises
Suppose we now decrease the initial object distance to 58 cm. Applying the lens
equation, we find s1’ = 2.48m
Lens separation = 2 m What is the object distance s2 for lens 2? (A) s2 = 0.48 m (B) s2 = +0.48 m (C) s2 = 2.48 m s1 = 58 cm
58
f = 47 cm
s1’ = 2.48 m BB (D) s2 = +2.48 m (E) s2 = +2.58 m THE OBJECT FOR THE SECOND LENS
IS THE IMAGE OF THE FIRST LENS s2 = 0.48
OR
s2 = +0.48 Image of first lens is a
Image
VIRTUAL object for the
second lens
second Physics 212 Lecture 28, Slide 21
21 Multiple Lenses Exercises
Suppose we now decrease the initial object distance to 58 cm.
Applying the lens equation, we find s1’ = 2.48m
BB Lens separation = 2 m s1=58 cm
f=47 cm
s1’ = 2.48 m
s2 = 0.48 m What is the nature of the FINAL image in terms of the ORIGINAL object?
(A) REAL
UPRIGHT (B) REAL
INVERTED fs2
s2 − f s2 < 0
M2 = − s2′
s2 (D) VIRTUAL
INVERTED PICTURES EQUATIONS
s2′ = (C) VIRTUAL
UPRIGHT Draw Rays as above
s2’ > 0 real image RESULTS
s2’ = 0.24 m M2 > 0 M = M1M2 < 0 M = 2.1 inverted image
Physics 212 Lecture 28, Slide 22
22 Course Review on Tuesday
• The Topics You Want to See
–
–
–
–
–
–
–
– Electric Fields/Gauss’ Law/Potential (34%)
Faraday’s Law (12%)
RC/RL Circuits (14%)
AC Circuits (11%)
Geometric Optics (13%)
Magnetic Fields & Forces (7%)
Electromagnetic Waves/Polarization (8%)
DC Circuits (3%) • Notes on the End Game • Final Exam: 50 questions uniformly covering topics in course • may still be able to change (combined (Dec 15)/conflict (Dec 16))
• About 40 students still have not registered their iclicker
About
iclicker
• Do it now or accept all zeroes for lectures
• Course Grade: See “Course Description” link on homepage
Course
Physics 212 Lecture 28, Slide 23
23 ...
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 Spring '11
 MESTRE
 Physics

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