Question related to Bragg law

  • Thread starter Roula
  • Start date
  • Tags
    Bragg Law
In summary, the wavelength of the incident wave must be smaller than the dimension of the sample in order for Bragg's Law to be applicable. This is due to the fact that waves do not scatter unless the wavelength is on the same order or smaller than the feature being investigated. This can be seen through the Huygens-Fresnel principle and is also mentioned in Newton's book on scattering theory.
  • #1
Roula
6
0
Hello everyone
I would like to ask you something related to the investigation of materials depending on Bragg Diffraction (Bragg Law).

It is a prerequisite, that the wavelength of the used radiation must be smaller than the dimension of the sample, by the meaning λ ≤ d , where λ is the wavelength and d is the interplaner spacing .

I know from Bragg law nλ=2dsinθ, that wavelength must be smaller than d in order to apply this law. But i can not understand physically the reason of that.
What is the physical reason that λ ≤ d ?

I am thankful for you all.

Roula
 
Physics news on Phys.org
  • #2
simply, waves do not scatter unless the wavelength of incident wave is on the order or smaller than the feature you want to investigate.

if that were the case, you would not be able to listen to the radio in your house because the radio waves would be scattered by your wall thickness...
 
  • #3
Dear Dr. Transport.
i am thankful for your response.

You are right that the wavelength must be smaller than the dimension to get scattered. And that was my question.

Could you please prove it for me ?
does the proof relate to Huygens–Fresnel principle ?

thanks again.
Roula
 
  • #4
No answer :(
 
  • #5
The wavelength don't has to be smaller than d for Bragg's law to be valid. It's just so that for λ<d the equation has the only solution n=0 and θ=0, i.e. the only possible solution is an unscattered wave.
 
  • #6
Check Newton's book, scattering theory of particles and waves.
 

1. What is the Bragg law and what does it describe?

The Bragg law, named after British physicists William and Lawrence Bragg, describes the relationship between the diffraction angle of X-rays and the spacing of atomic planes in a crystal lattice. It states that when an X-ray beam is incident on a crystal at a specific angle, the X-rays will be diffracted in a way that constructive interference occurs between the X-rays reflected from adjacent atomic planes.

2. How is the Bragg law used in X-ray crystallography?

The Bragg law is used in X-ray crystallography to determine the atomic and molecular structure of crystals. By measuring the diffraction pattern of X-rays that are scattered by the crystal, the spacing of the atomic planes can be calculated using the Bragg law. This information can then be used to determine the positions of the atoms within the crystal lattice.

3. What factors can affect the accuracy of the Bragg law in X-ray crystallography?

Several factors can affect the accuracy of the Bragg law in X-ray crystallography, including the quality of the crystal sample, the wavelength of the X-rays, and the precision of the measuring equipment. The orientation of the crystal and the presence of defects or imperfections in the crystal lattice can also impact the accuracy of the diffraction pattern and therefore the calculations based on the Bragg law.

4. Can the Bragg law be applied to materials other than crystals?

Yes, the Bragg law can be applied to any material with a regularly repeating structure, not just crystals. This includes materials such as fibers, films, and powders. However, the material must have a periodic arrangement of atoms in order for the Bragg law to be applicable.

5. What are some practical applications of the Bragg law?

The Bragg law has a wide range of practical applications, including X-ray crystallography for determining the structure of proteins and other molecules, as well as in materials science for studying the atomic structure of materials such as metals and ceramics. It is also used in non-destructive testing techniques, such as X-ray diffraction imaging, to analyze the internal structure of objects without damaging them.

Similar threads

Replies
2
Views
2K
  • Atomic and Condensed Matter
Replies
4
Views
2K
  • Advanced Physics Homework Help
Replies
1
Views
954
  • Advanced Physics Homework Help
Replies
1
Views
2K
  • Introductory Physics Homework Help
Replies
2
Views
1K
  • Atomic and Condensed Matter
Replies
4
Views
1K
  • Atomic and Condensed Matter
Replies
5
Views
3K
  • Atomic and Condensed Matter
Replies
9
Views
2K
  • Introductory Physics Homework Help
Replies
1
Views
2K
  • Atomic and Condensed Matter
Replies
4
Views
2K
Back
Top