Transcript Single Slit Diffraction (8/5)

Chapter 35
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Interference (cont.)
Interference in thin films
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Figure 35.11 (right)
shows why thin-film
interference occurs,
with an illustration.
Figure 35.12 (below)
shows interference of
an air wedge.
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Phase shifts during reflection
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Follow the text analysis of thin-film interference and
phase shifts during reflection. Use Figure 35.13 below.
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Q35.6
An air wedge separates two
glass plates as shown. Light of
wavelength l strikes the upper
plate at normal incidence. At a
point where the air wedge has
thickness t, you will see a
bright fringe if t equals
A. l/2.
B. 3l/4.
C. l.
D. either A. or C.
E. any of A., B., or C.
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A35.6
An air wedge separates two
glass plates as shown. Light of
wavelength l strikes the upper
plate at normal incidence. At a
point where the air wedge has
thickness t, you will see a
bright fringe if t equals
A. l/2.
B. 3l/4.
C. l.
D. either A. or C.
E. any of A., B., or C.
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Newton’s rings
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Figure 35.16 below illustrates the interference
rings (called Newton’s rings) resulting from an air
film under a lens.
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Using interference fringes to test a lens
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The lens to be
tested is placed
on top of the
master lens. If
the two
surfaces do not
match,
Newton’s rings
will appear, as
in Figure 35.17
at the right.
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Chapter 36
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Diffraction
Diffraction
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According to geometric optics, a light source shining on an
object in front of a screen should cast a sharp shadow.
Surprisingly, this does not occur because of diffraction.
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Diffraction and Huygen’s Principle
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Fresnel diffraction: Source, screen, and obstacle are close
together.
Fraunhofer diffraction: Source, screen, and obstacle are far apart.
Figure 36.2 below shows the diffraction pattern of a razor blade.
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Diffraction from a single slit
• In Figure 36.3 below, the prediction of geometric optics in
(a) does not occur. Instead, a diffraction pattern is produced,
as in (b).
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Fresnel and Fraunhofer diffraction by a single slit
• Figure 36.4 below shows Fresnel (near-field) and
Frauenhofer (far-field) diffraction for a single slit.
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Locating the dark fringes
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Figure 36.5 below shows the geometry for Fraunhofer
diffraction.
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An example of single-slit diffraction
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Figure 36.6 (bottom left) is a photograph of a
Fraunhofer pattern of a single horizontal slit.
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Intensity maxima in a single-slit pattern
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Figure 36.9 at the right shows the
intensity versus angle in a single-slit
diffraction pattern.
Part (b) is photograph of the
diffraction of water waves.
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Width of the single-slit pattern
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The single-slit diffraction pattern depends on the ratio of
the slit width a to the wavelength l. (Figure 36.10 below.)
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Q36.1
Light of wavelength l passes through a single slit
of width a. The diffraction pattern is observed on
a screen that is very far from from the slit.
Which of the following will give the greatest
increase in the angular width of the central
diffraction maximum?
A. Double the slit width a and double the wavelength l.
B. Double the slit width a and halve the wavelength l.
C. Halve the slit width a and double the wavelength l.
D. Halve the slit width a and halve the wavelength l.
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A36.1
Light of wavelength l passes through a single slit
of width a. The diffraction pattern is observed on
a screen that is very far from from the slit.
Which of the following will give the greatest
increase in the angular width of the central
diffraction maximum?
A. Double the slit width a and double the wavelength l.
B. Double the slit width a and halve the wavelength l.
C. Halve the slit width a and double the wavelength l.
D. Halve the slit width a and halve the wavelength l.
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Q36.2
In a single-slit diffraction experiment with waves of
wavelength l, there will be no intensity minima (that is,
no dark fringes) if the slit width is small enough.
What is the maximum slit width a for which this occurs?
A. a = l/2
B. a = l
C. a = 2l
D. The answer depends on the distance from the slit to
the screen on which the diffraction pattern is viewed.
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A36.2
In a single-slit diffraction experiment with waves of
wavelength l, there will be no intensity minima (that is,
no dark fringes) if the slit width is small enough.
What is the maximum slit width a for which this occurs?
A. a = l/2
B. a = l
C. a = 2l
D. The answer depends on the distance from the slit to
the screen on which the diffraction pattern is viewed.
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Two slits of finite width
• For slits extremely
narrow, behaves very
close to ideal case from
previous chapter
• For wider slits, behaves
like a combination of
single-slit diffraction and
double-slit interference.
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Interference pattern of several slits
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Figure 36.15 below shows the interference pattern for 2, 8, and 16
equally spaced narrow slits.
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Q36.3
In Young’s experiment, coherent light passing through
two slits separated by a distance d produces a pattern of
dark and bright areas on a distant screen.
If instead you use 10 slits, each the same distance d
from its neighbor, how does the pattern change?
A. The bright areas move farther apart.
B. The bright areas move closer together.
C. The spacing between bright areas remains the same,
but the bright areas become narrower.
D. The spacing between bright areas remains the same,
but the bright areas become broader.
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A36.3
In Young’s experiment, coherent light passing through
two slits separated by a distance d produces a pattern of
dark and bright areas on a distant screen.
If instead you use 10 slits, each the same distance d
from its neighbor, how does the pattern change?
A. The bright areas move farther apart.
B. The bright areas move closer together.
C. The spacing between bright areas remains the same,
but the bright areas become narrower.
D. The spacing between bright areas remains the same,
but the bright areas become broader.
© 2012 Pearson Education, Inc.