Diffraction
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Understanding Diffraction: Shadows, Slits, and Circular Holes, Slides of Physics
The concept of diffraction, focusing on the effects of slits and circular holes on wave behavior. Topics include the relationship between wavelength and shadow formation, huygen's principle, diffraction minima, and fraunhofer diffraction. Understand the principles behind these phenomena and the resulting patterns.
Typology: Slides
2012/2013
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Diffraction
Obstacles
Small wavelength waves thatencounter a large object leavea shadow area behind theobject.
Large wavelength waves thatencounter an object leave lessshadow area.
This is called
diffraction
Return to Huygen
Huygen’s principle composedwavefronts from individualscattering points.
•^
Converted to rays
For a narrow opening there isinterference within theopening.
•^
Nodes and antinodes
This can be viewed as raysfrom points in the slit.
Diffraction Minima
A ray from the middle is behinda ray from the top.
•^
Offset by
a
/2 sin
•^
Could cause cancelation
Each point below would alsodestructively interfere.
•^
Intensity minimum
2
sin 2
a
^
sin a
Circular Hole
Fraunhofer patterns aresymmetric around the opening.
A circular hole produces ringsaround a central maximum.
•^
Airy disk
-^
84% of energy in center
Resolution
An Airy disk has a radius thatdepends on the size of theopening.
•^
Aperture diameter
D
•^
Circular lens focal length
f
D
f
r
(^22). 1
D
^
(^22). 1
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