phy2049 summer 2011
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PHY2049 Summer 2011. The following clicker numbers are no longer going to be counted. They have not been registered. 420441461211462681 497478625833 Exam 2 (Ch. 28-33 ) is scheduled for Monday July 11 during class times. Images. Chapter 34 - PowerPoint PPT PresentationTRANSCRIPT
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PHY2049 Summer 2011
• The following clicker numbers are no longer going to be counted. They have not been registered.
420441 461211 462681
497478 625833• Exam 2 (Ch. 28-33) is scheduled for
Monday July 11 during class times.
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Chapter 34
One of the most important uses of the basic laws governing light is the production of images. Images are critical to a variety of fields and industries ranging from entertainment, security, and medicine
In this chapter we define and classify images, and then classify several basic ways in which they can be produced.
Images
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A clear sheet of polaroid is placed on top of a similar sheet so that their polarizing axes make an angle of 30◦ with each other. The ratio of the intensity of emerging light to incident unpolarized light is:
A. 1/4 B. 1/3 C. 1/2 D. 3 /4 E. 3 /8
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Image: a reproduction derived from light
Real Image: light rays actually pass through image, really exists in space (or on a screen for example) whether you are looking or not
Virtual Image: no light rays actually pass through image. Only appear to be coming from image. Image only exists when rays are traced back to perceived location of source
Two Types of Images
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object lensreal image
object mirror virtual image
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Light travels faster through warm air warmer air has smaller index of refraction than colder air refraction of light near hot surfaces
For observer in car, light appears to be coming from the road top ahead, but is really coming from sky.
A Common Mirage
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Fig. 34-1
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Plane mirror is a flat reflecting surface.
Plane Mirrors, Point Object
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Fig. 34-2
Fig. 34-3
Ib Ob
Identical triangles
Plane Mirror: i pSince I is a virtual image i < 0
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Each point source of light in the extended object is mapped to a point in the image
Plane Mirrors, Extended Object
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Fig. 34-4 Fig. 34-5
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Your eye traces incoming rays straight back, and cannot know that the rays may have actually been reflected many times
Plane Mirrors, Mirror Maze
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Fig. 34-6
1
23
4
56
78
9
12
34
56
78
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Plane mirror Concave Mirror1. Center of Curvature C:
in front at infinity in front but closer2. Field of view
wide smaller3. Image
i=p |i|>p 4. Image height
image height = object height image height > object height
34-Fig. 34-7
Plane mirror Convex Mirror1. Center of Curvature C:
in front at infinity behind mirror and closer2. Field of view
wide larger3. Image
i=p |i|<p 4. Image height
image height = object height image height < object height
Spherical Mirrors, Making a Spherical Mirror
concave
plane
convex
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Spherical Mirrors, Focal Points of Spherical Mirrors
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Fig. 34-8
concave convex
Spherical Mirror:1
2f r
r > 0 for concave (real focal point)r < 0 for convex (virtual focal point)
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Start with rays leaving a point on object, where they intersect, or appear to intersect marks the corresponding point on the image.
Images from Spherical Mirrors
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Fig. 34-9
Real images form on the side where the object is located (side to which light is going). Virtual images form on the opposite side.
Spherical Mirror:1 1 1
p i f Lateral Magnification:
'hm
h
Lateral Magnification:i
mp
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Locating Images by Drawing Rays
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Fig. 34-10
1. A ray parallel to central axis reflects through F2. A ray that reflects from mirror after passing through F, emerges parallel to central axis3. A ray that reflects from mirror after passing through C, returns along itself4. A ray that reflects from mirror after passing through c is reflected symmetrically about the
central axis
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Proof of the magnification equation
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Fig. 34-10
Similar triangles (are angles same)
, ,
(magnification)
de cd decd i ca p m
ab ca abi
mp
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Spherical Refracting Surfaces
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Fig. 34-11
Real images form on the side of a refracting surface that is opposite the object (side to which light is going). Virtual images form on the same side as the object.
Spherical Refracting Surface: 1 2 2 1n n n n
p i r
When object faces a convex refracting surface r is positive. When it faces a concave surface, r is negative. CAUTION: Reverse of of mirror sign convention!
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Fig. 34-13
Converging lens
Diverging lens
Thin Lens:1 1 1
f p i Thin Lens in air:
1 2
1 1 11n
f r r
Lens only can function if the index of the lens is different than that of its surrounding medium
Thin Lenses
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Images from Thin Lenses
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Fig. 34-14
Real images form on the side of a lens that is opposite the object (side to which light is going). Virtual images form on the same side as the object.
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Locating Images of Extended Objects by Drawing Rays
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Fig. 34-15
1. A ray initially parallel to central axis will pass through F22. A ray that initially passes through F1, will emerge parallel to central axis3. A ray that initially is directed toward the center of the lens will emerge from the lens
with no change in its direction (the two sides of the lens at the center are almost parallel)
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Two Lens System
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1. Let p1 be the distance of object O from Lens 1. Use equation and/or principle rays to determine the distance to the image of Lens 1, i1.
2. Ignore Lens 1, and use I1 as the object O2. If O2 is located beyond Lens 2, then use a negative object distance p1. Determine i2 using the equation and/or principle rays to locate the final image I2.
Lens 1 Lens 2
p1
OI1
i1
O2
p2
I2
i2
1 2The net magnification is: M m m
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A football field is about 100 meters long. The time for light to travel this distance is about:
A. 0.33x10-6 s B. 0.33 ms C. 33 minD. 3 hr E. 3 yr
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Optical Instruments, Simple Magnifying Lens
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Fig. 34-17
Can make an object appear larger (greater angular magnification) by simply bringing it closer to your eye. However, the eye cannot focus on objects closer that the near point pn~25 cmBIG & BLURRY IMAGE
A simple magnifying lens allows the object to be placed close by making a large virtual image that is far away.
'
and '25 cm
m
h h
f
Simple Magnifier:
25 cmm
f
Object at F1
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2134-
Fig. 34-18
Optical Instruments, Compound Microscope
obob
ob ey
since and
25 cm magnification compounded (microscope)
i sm i s p f
p f
sM mm
f f
I close to F1’O close to F1
Mag. Lens
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Optical Instruments, Refracting Telescope
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Fig. 34-19
eyob ey
ob ob ey
ob
ey
' ' , ,
(telescope)
h hm
f f
fm
f
I close to F2 and F1’
Mag. Lens
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Three Proofs, The Spherical Mirror Formula
34-
Fig. 34-20
and 2
1
2
,
12
2
1 1 1
2
22
ac ac ac ac
cO p cC r
ac ac
CI i
f r
ac ac ac
p i
r f
pf i f
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Three Proofs, The Refracting Surface Formula
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Fig. 34-21
1 1 2 2
1 1 2 2 1 2
1 2
1 2
1 2 2 1
1 2 2
1 2 2 1
1
sin sin
if and are small
and
; ;
n n n n
ac ac acn n n
n n
n n
n
np
n
ac ac ac
p r i
n n n n
p i
i
r
r
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2534-
Fig. 34-22
1 2 2 1
1 2
where 1 and
'' '
1 1 ; if small
1 1 Eq. 34-22
' ' '
1 1 Eq. 34-25
' '' ''
Eq. 34-22 Eq. 34
' '' ''1 1 1 1 1 1 1 1
1 1' '' ' '
-25' ' ''
n n n n
p i r
n n n
p i L
n nL
i L i r
n np i r r p
n n
p i r
n n
i r
i i
r
r
Three Proofs, The Thin Lens Formulas
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The time for a radar signal to travel to the Moon and back, a one-way distance of about 3.8 × 108 m, is:
A. 1.3 s B. 2.5 s C. 8 s D. 8minE. 1 × 106 s
Radio waves of wavelength 3 cm have a frequency of:
A. 1MHz B. 9MHz C. 100MHz D. 10, 000MHz E. 900MHz
The light intensity 10m from a point source is 1000W/m2. The intensity 100m from the samesource is:
A. 1000W/m2 B. 100W/m2 C. 10W/m2 D. 1W/m2
E. 0.1W/m2
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Light of uniform intensity shines perpendicularly on a totally absorbing surface, fully illuminating the surface. If the area of the surface is decreased:
A. the radiation pressure increases and the radiation force increasesB. the radiation pressure increases and the radiation force decreasesC. the radiation pressure stays the same and the radiation force increasesD. the radiation pressure stays the same and the radiation force decreasesE. the radiation pressure decreases and the radiation force decreases