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Reflected image
• Draw one ray from the object
that enters the eye after
reflecting from the mirror. Is
this one ray sufficient to tell
you eye/brain where the
image is located?
• Draw another ray to locate
and label the image point.
• Do any of the rays that enter
the eye actually pass through
the image point?
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Constructing the image from a plane mirror II
• Images from a plane mirror show left/right reversal.
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Reflection and refraction
• Figure 33.5 illustrates both reflection and refraction at once. The
storefront window both shows the passersby their reflections and allows
them to see inside.
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Q33.2
Light passes from vacuum (index of refraction n = 1) into
water (n = 1.333).
If the incident angle qa is in the range 0° < qa < 90°,
A. the refracted angle is greater than the incident angle.
B. the refracted angle is equal to the incident angle.
C. the refracted angle is less than the incident angle.
D. the answer depends on the specific value of qa .
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A33.2
Light passes from vacuum (index of refraction n = 1) into
water (n = 1.333).
If the incident angle qa is in the range 0° < qa < 90°,
A. the refracted angle is greater than the incident angle.
B. the refracted angle is equal to the incident angle.
C. the refracted angle is less than the incident angle.
D. the answer depends on the specific value of qa .
Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley
Q33.3
Light passes from a medium of index of refraction na into a
second medium of index of refraction nb. The angles of
incidence and refraction are qa and qb respectively.
If na < nb,
Aqa > qb and the light speeds up as it enters the second medium.
B. qa > qb and the light slows down as it enters the second medium.
C. qa < qb and the light speeds up as it enters the second medium.
D. qa < qb and the light slows down as it enters the second medium.
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A33.3
Light passes from a medium of index of refraction na into a
second medium of index of refraction nb. The angles of
incidence and refraction are qa and qb respectively.
If na < nb,
Aqa > qb and the light speeds up as it enters the second medium.
B. qa > qb and the light slows down as it enters the second medium.
C. qa < qb and the light speeds up as it enters the second medium.
D. qa < qb and the light slows down as it enters the second medium.
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Why should the ruler appear to be bent?
•
The difference in index of refraction for air and water causes your
eye to be deceived. Your brain follows rays back to the origin they
would have had if not bent.
•
Consider Figure 33.9.
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Prism
Complete rays through the two prisms shown.
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Why should sunsets be orange and red?
•
The light path at sunset is much longer than at noon when the sun is
directly overhead.
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Dispersion
• From the discussion of the
prism seen in earlier slides,
we recall that light refraction
is wavelength dependent.
This effect is made more
pronounced if the index of
refraction is higher. “Making
a rainbow” is actually more
than just appreciation of
beauty; applied to chemical
systems, the dispersion of
spectral lines can be a
powerful identification tool.
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Goldfish
You are looking at a goldfish in a fish tank from
the top. It appears that the fish is 30 degrees
below the horizontal. Where is the fish?
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Q33.4
Light passes from a medium of index of refraction na into a
second medium of index of refraction nb. The critical angle for
total internal reflection is qcrit.
In order for total internal reflection to occur, what must be true
about na, nb, and the incident angle qa?
A. na > nb and qa > qcrit
B. na > nb and qa < qcrit
C. na < nb and qa > qcrit
D. na < nb and qa < qcrit
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A33.4
Light passes from a medium of index of refraction na into a
second medium of index of refraction nb. The critical angle for
total internal reflection is qcrit.
In order for total internal reflection to occur, what must be true
about na, nb, and the incident angle qa?
A. na > nb and qa > qcrit
B. na > nb and qa < qcrit
C. na < nb and qa > qcrit
D. na < nb and qa < qcrit
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Goldfish 2
•Describe what a goldfish sees if another fish
swims directly overhead and moves past the
angle of total internal reflection. Where is this
point of total internal reflection?
•Is there a spot where you cannot see the goldfish
looking down from the top of the tank?
•Is there a way where you can see the goldfish,
but the fish can’t see you?
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Thin lenses I
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Thin lenses and focal point
•Continue the rays through lens and out other side.
•Is the point where the rays converge the same as the focal point or
different?
•Place a point source at the place where the rays converged. Draw
several rays heading left through the lens. Do these rays converge?
Would an image form?
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Q34.8
An object PQ is placed
in front of a converging
lens, forming a real
image P´Q´. If you use
black paint to cover the
lower half of the lens,
A. only the object’s upper half will be visible in the image.
B. only the object’s lower half will be visible in the image.
C. only the object’s left-hand half will be visible in the image.
D. only the object’s right-hand half will be visible in the image.
E. the entire object will be visible in the image.
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A34.8
An object PQ is placed
in front of a converging
lens, forming a real
image P´Q´. If you use
black paint to cover the
lower half of the lens,
A. only the object’s upper half will be visible in the image.
B. only the object’s lower half will be visible in the image.
C. only the object’s left-hand half will be visible in the image.
D. only the object’s right-hand half will be visible in the image.
E. the entire object will be visible in the image.
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Thin lenses and images
f1
f2
•An object is placed to the left of the focal point, f1. Where is its
image and is the image inverted or upright? Label s, s’. Are they
positive or negative?
•An object is placed between the lens and the focal point, , f1. Where
is its image and is the image inverted or upright? Label s, s’. Are they
positive or negative?
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Thin lenses II
•
Figure 34.31 at bottom left illustrates a diverging lens scattering light rays and
the position of its second (virtual) focal point.
•
Figure 34.32 illustrates some assorted common arrangements of lens surfaces.
•
Follow Example 34.8.
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Graphical methods for lenses
•
Figure 34.36 applies to lenses the same ray-tracing method we used for
mirrors.
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Magnifying lens
A magnifying lens with focal length 15cm is used
to magnify an ant which is 10 cm away.
• Draw a ray diagram of this situation
• Calculate the distance the image is away from
the lens
• How big does the 2 mm long ant appear?
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The camera
• A clever
arrangement of
optics with a
method to record
the inverted image
on its focal plane
(sometimes film,
sometimes an
electronic
array, it depends
on your camera).
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The eye—vision problems
•
When the lens of the eye
allows incoming light to
focus in front of or behind
the plane of the retina, a
person’s vision will not be
sharp.
•
Figure 34.45 (at right) shows
normal, myopic, and
hyperopic eyesight.
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Vision correction—examples
•
Follow Example 34.13, illustrated in Figure 34.49 in the middle of the
page.
•
Follow Example 34.14, illustrated in Figure 34.50 at the bottom of the
page.
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The microscope
•
Optical elements are arranged to magnify tiny images for visual
inspection. Figure 34.52 presents the elements of an optical
microscope.
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The astronomical telescope
•
Optical elements are arranged to magnify distant objects for visual
inspection. Figure 34.53 presents the elements of an astronomical
telescope.
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The reflecting telescope
•
Optical elements are arranged to reflect collected light back to an
eyepiece or detector. This design eliminates aberrations more likely
when using lenses. It also allows for greater magnification. The
reflective telescope is shown in Figure 34.54.
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Special case—dispersion and atmospheric rainbows
•
As a person looks
into the sky and sees
a rainbow, he or she
is actually “receiving
light signals” from a
physical spread of
water droplets over
many meters (or
hundreds of meters)
of altitude in the
atmosphere. The reds
come from the higher
droplets and the
blues from the lower
(as we have seen in
the wavelength
dependence of light
refraction).
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Selecting one orientation of the EM wave—the Polaroid
•
A Polaroid filter is a polymer array that can be thought of like teeth in
a comb. Hold the comb at arm’s length with the teeth pointing down.
Continue the mental cartoon and imagine waves oscillating straight up
and down passing without resistance. Any “side-to-side” component
and they would be blocked.
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Polarization I
• Read Problem-Solving Strategy 33.2.
• Follow Example 33.5.
• By reflection from a surface? Read pages 1139 and 1140 and
then refer to Figure 33.27 below.
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Polarization II
• Consider Figure 33.28.
• Follow Example 33.6, illustrated by Figure 33.29.
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