Confusion about Fraunhofer Diffraction

In summary, the conversation discusses the explanation for single slit Fraunhofer diffraction, specifically the location of intensity minima. The variables involved are a (slit width), lambda (wavelength), and theta (angle). By dividing the slit into two or four parts and viewing the wavefront as a sum of small sources, it is understood that a*sin(theta)/2=lambda/2 and a*sin(theta)=2*lambda lead to constructive interference. However, when a*sin(theta)=2*lambda and the slit is divided into two regions, the same logic does not apply and there is full constructive interference. The individual is seeking clarification on this discrepancy and suggests looking at a graphical approach for better understanding.
  • #1
Zarquon
20
0
I'm looking at the explanation for single slit Fraunhofer diffraction, in particular the location of the intensity minima. a is the slit width, lambda is the wavelength and theta is the angle. By dividing the slit into two parts and viewing the wavefront as a sum of many small sources i can see that everything cancels out when a*sin(theta)/2=lambda/2. I also see why the same happens for a*sin(theta)=2*lambda, by dividing the slit into four regions. However: If we let a*sin(theta)=2*lambda, and instead divide the slit into two regions as before, it looks to me like we get full constructive interference by using the same logic as in the case of the first minima. I know I'm making som basic mistake here, just can't figure it out. Hope somebody can make sense of this. [It's a little hard for me to explain the problem, but i hope someone who is familiar with the explanation i am talking about (from University Physics by Young and Friedman btw) might understand the question.]
 
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  • #2
Have you looked at a graphical approach to the problem?

sinint8.gif


http://hyperphysics.phy-astr.gsu.edu/hbase/phyopt/sinint.html
 
  • #3
Thanks! I see now why my reasoning is wrong.
 

What is Fraunhofer Diffraction?

Fraunhofer Diffraction is a phenomenon that occurs when a wave, such as light or sound, passes through an aperture or around an object and spreads out to form a diffraction pattern. It was first observed by Joseph von Fraunhofer in the early 19th century.

What causes confusion about Fraunhofer Diffraction?

Confusion about Fraunhofer Diffraction often arises because it is commonly confused with another diffraction phenomenon known as Fresnel diffraction. While both involve the spreading of waves, they occur under different conditions and produce different patterns.

What are the key differences between Fraunhofer and Fresnel diffraction?

The key differences between Fraunhofer and Fresnel diffraction are the distance between the source and the diffracting object, the distance between the object and the screen, and the size of the diffracting object relative to the wavelength of the wave. Fresnel diffraction occurs when the source and screen are close to the diffracting object and the object is larger than the wavelength, while Fraunhofer diffraction occurs when the source and screen are far from the object and the object is smaller than the wavelength.

How is Fraunhofer Diffraction used in science and technology?

Fraunhofer Diffraction has many applications in science and technology, particularly in the fields of optics and acoustics. It is used to study the properties of waves, such as their wavelength and amplitude, and to create diffraction gratings which are used in spectroscopy and optical devices such as cameras and telescopes.

What are some real-world examples of Fraunhofer Diffraction?

Fraunhofer Diffraction can be observed in many everyday situations, such as when light passes through a narrow slit in a window blind and creates a diffraction pattern on the floor or wall, or when sound waves pass through a small opening in a building and create a diffraction pattern on the other side. It is also commonly seen in the colorful patterns produced by CDs and DVDs, which use diffraction gratings to read and store data.

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