Major Concepts of Physics PHY102

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• Major Concepts of Physics PHY102

Lecture 5Squeezing light through narrow holes.
Diffraction January 28th Spring 2009 Prof.
Liviu Movileanu http//physics.syr.edu/courses/PHY
102.07Spring/index.html lmovilea_at_physics.syr.edu
Room 211, Physics Bldg., 443-8078
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Major Concepts of Physics PHY102 Lecture 5
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Lecture objectives
1. Introduction to diffraction. Huygenss
principle ?Big deal! What is the fundamental
condition for wave optics (interference,
diffraction)? 2. Single-slit diffraction ?Experi
mental hypothesis ?Single-slit experiment
(Experimental evidence) ?Diffraction patterns
(Interpretation) ?Compare interference with
diffraction patterns 3. Lecture demonstration
(single-slit interference) 4. Diffraction and
the resolution of optical instruments 5.
Announcements/Homework
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Introduction to Diffraction
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Diffraction The fundamental condition
a. Pertinent to geometrical optics -- d gtgt ? b.
Pertinent to wave optics -- ? ? d
d
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Introduction to Diffraction
 
b. Circular hole --- Spherical waves c.
Rectangular slit --- Cylindrical waves
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Diffraction patterns
                           
 
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Grimaldis work
                       
On close examination of the edges, we find
There are alternate regions of darkness and
brightness.   First known discovery of
diffraction  Observations by Francesco Grimaldi,
a Jesuit priest, (1618 1663).   He looked at
sunlight entering a darkened room through a tiny
hole in a screen.   Found The spot was
enlarged, relative to expectations from a
particle model of light.   He examined the border
of the image. Observed Colored fringes.
Grimaldis work was the first experimental
evidence that light is a wave.
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From an experimental point-of-view, there are two
signposts of diffraction When light goes
through a small opening, it spreads out like a
fan.There is no sharp shadow. Instead, the
image is blurred at its edges. The same
statements hold, when light encounters an
obstacle. Again, there is no sharp shadow.
Diffraction a brief review

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Announcement
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(a/2)sin?m(?/2) first minimum
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Rayleighs criterion
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Observation of diffraction
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Example 25.8 Continuation
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Example 25.8 Continuation

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Example 25.9
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Applications of diffraction X-ray diffraction
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Announcements

• 1. Reading Chapter 25th, Sections 25.6, 25.7,
  25.8 (pages 929-937). Conceptual examples 25.7,
  25.8 and 25.9
• 2. Homework for the next week (on paper) Please
  pick up the print outs today. The homework 2 is
  due next weeks workshop.
• 3. Do you want to be challenged? More MCAT preps?
• Problems 25.7 Diffraction by a single slit
• Problems 25.8 Diffraction and the resolution of
  optical instruments
• 4. This weeks lab Interference and Diffraction

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