What is Bragg's law: Definition and 30 Discussions

In physics, Bragg's law, Wulff–Bragg's condition or Laue-Bragg interference, a special case of Laue diffraction, gives the angles for coherent scattering of waves from a crystal lattice. It encompasses the superposition of wave fronts scattered by lattice planes, leading to a strict relation between wavelength and scattering angle, or else to the wavevector transfer with respect to the crystal lattice. Such law had initially been formulated for X-rays upon crystals but is moreover relevant for all kind of quantum beams, such as neutron and electron waves on atomic spacing, as well as for visual light on artificial periodic micro-scale lattices.

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  1. Dario56

    I Questions About Bragg's Law of X-Ray Diffraction

    Bragg's law is schematically shown on the picture: Two parallel and plane waves are shown which propagate towards the crystal. For plane waves, wave fronts are flat planes perpendicular to the wave propagation with infinite size. In reality, there are no plane waves. Nevertheless, they are...
  2. B

    Finding angles with Bragg's Law

    Part (a) Ok so for (a) ##\theta_{incident} = \theta_{reflected}##, so I assume I could just consider the horizontal planes in these atoms. ##n\lambda = 2a\sin(\theta)## ##p = \frac {h} {\lambda}## ##\frac {nh} {2amv} = \sin(\theta)## ## v = \frac {nh} {2am\sin(\theta)}## I suppose the...
  3. U

    X-ray Diffraction and Bragg's Law

    Hi, I know the material being studied is FeCO3.H20 (hydrated siderite) and the wavelength for a D2 diffractometer with a Co tube is 1.79026. In order to use Bragg's Law to calculate the peak positions, I think I need to first calculate d using the equation with the Miller indices and a which...
  4. C

    Bragg diffraction form an “inclined” crystal plane

    Homework Statement In picture, first-order reflection from the reflection planes shown occurs when an x-ray beam of wavelength ##0.260 nm## makes an angle ##\theta=63.8°## with the top face of the crystal. What is the unit cell size ##a_0##? Homework Equations Bragg law $$d=\frac{ n...
  5. M

    X-ray diffraction and Bragg's law

    Homework Statement The Attempt at a Solution Hi All, I have two issues with this question. First of all when I put the given values into the Bragg condition for diffraction I get two different wavelengths when the question implies there is only one. Secondly, I don't know how I can...
  6. L

    Determining which energy level transfers cause peaks in x-ray spectra

    Hi all, I'm wondering how, for each peak in an x-ray spectra from a material (and using a crystal analyser), it is determined which energy level jump the peak corresponds to? How would you figure out the correct value of n to substitute into Bragg's Law to find the energy of the beam? Thank you!
  7. L

    I X-ray diffraction minima?

    For x-day diffraction maxima we have braggs law 2d*sinθ = mλ (maxima) Is there an analogous law for the minima like 2d*sinθ = (m+1/2)λ (minima?) Thanks!
  8. J

    Electron Scattering and Bragg's law

    Homework Statement A beam of thermal neutrons (K = 0.025 eV) scatters from a crystal with interatomic spacing 0.45 nm. What is the φ angle of the first order Bragg peak? (as defined in figure 5.11, φ and the scattering angle add up to 180 degrees). Homework Equations nλ = 2dsinθ = DsinΦ d...
  9. T

    Calculating Bragg Angles for X-Ray Scattering from Table Salt Crystal

    Homework Statement The Spacing between the Na and Cl atoms in table salt (NaCl) is ##d=2.82x10^{-10}m##, which was first deduced from Bragg scattering. For an experiment where X-rays of energy 20 eV are produced, what are the corresponding Bragg angles below ##90^{\circ}## for scattering from a...
  10. adamaero

    Crystallography, diffraction, identifying the pure element

    Homework Statement The only things you know about the sample are: (i) it has some kind of cubic lattice, and (ii) it is a pure element. Identify the element in the crystalline sample. SC: R = 0.5a FCC: R = 0.25a√2 BCC: R = 0.25a√3 Distances from Bragg peaks: d1 = 0.2037 nm d2 = 0.1746 nm d3...
  11. saybrook1

    Bragg's Law with Refractive Correction

    Hi guys, the x-ray data booklet gives a modified Bragg's Law that seems to be a combination of Snell's and Braggs. I'll post a picture of what this looks like. I've tried combining the two equations and coming up with their answer but can't get a solid derivation. Any help or a point toward a...
  12. saybrook1

    A Understanding Modified Bragg's Law: A Guide with Derivation and Examples

    Hi guys, the x-ray data booklet gives a modified Bragg's Law that seems to be a combination of Snell's and Braggs. I'll post a picture of what this looks like. I've tried combining the two equations and coming up with their answer but can't get a solid derivation. Any help or a point toward a...
  13. Kelly Green

    Bragg's Law (X-Ray Analytical Methods)

    Homework Statement Explain using word, diagrams, and/or calculations.. (1) Why must n always be <= 2d/λ? (2) If λ is significantly greater then d, why will no diffraction occur? Homework Equations Bragg's Law nλ=2dsinθ n has its maximum when sinθ is 1 (at 90°) The Attempt at a Solution I am...
  14. MintyPanda

    Understanding Bragg's Law: The Relationship Between Wavelength & Atomic Order

    Hello, My teacher was talking about Bragg's law and mentioned how there was a relationship between the wavelength of light and a solid's order of separations. I'm still confused about this, actually. Can someone please help me clear up what he said? What is the order of separations in a solid...
  15. B

    Davisson-Germer experiment and Bragg's law

    In Davisson-Germer experiment the necessity of constructive interference is dsin(theta)=n(wavelenght) but in Braggs law its 2dsin(theta)=n(wavelenght), why are these two different? I saw that Braggs law is used between layers of crystals but I've also seen Davisson-Germer experiment's equation...
  16. S

    Bragg's law and the distribution of electromagnetic energy.

    While I get the coherent and incoherent scattering process that leads to the bragg diffraction condition, I don't really understand the physical mechanism behind the transmission and reflection. Now, as I understand it, the bragg diffraction condition is satisfied only for one or two particular...
  17. C

    Bragg's Law: Why is the equation not like this?

    Bragg's Law is well-known, and looks like the following: nλ = 2d \cdot sin(θ) , where d is the distance between the two crystal planes. This equation, or criteria, describes when constructive interference happens and an intensified, reflected ray can be measured at the same angle as the...
  18. T

    How can there be interference of light rays in Bragg's law

    As we know, Bragg's law is based on the path length difference between light which interfere with themselves after being scattered from atoms in the crystal. If you google "Bragg's law", you will see numbers of pictures showing two light rays being scattered from two different atoms. Those...
  19. S

    Solving Bragg's Law: X-Ray & Electron Measurement

    I'm preparing for a midterm exam and this is one of the practise questions I'm having a bit of trouble with. Homework Statement We have access to X-ray and electrons for the incident beam. \theta is the inner angle between the sample and the incident beam. Spacing in sample = d...
  20. R

    Bragg's Law in Crystallography

    I took a course on protein crystallography last year and there's one thing I couldn't figure out then, and still can't figure out now. My understanding of Bragg's law hinges on the fact that in-phase scattered waves constructively interfere, and the requirement to be in-phase is met only when...
  21. A

    Why Does Bragg's Law Require Integers?

    Hi there, So in bragg's law 2d\sin \theta =n\lambda, n needs to be an integer. Can anyone explain why? I mean, what if the extra path 2d that the 'second beam' has is not dividable by a wavelength? Not sure if this is asked before but could not find it! Cheers, Adnan
  22. fluidistic

    X-rays diffraction in a solid, Bragg's law

    Homework Statement The X-rays diffraction diagramm of a cubic crystal shows lines for the following angles 2 \delta = 31.47º, 39.74º, 47.58º, 64.71º and 77.59º when the X-rays have a wavelength of 1.54 \times 10 ^{-10}m. Determine the crystal stucture of the net, the Miller indices of the...
  23. O

    Bragg's Law: Find Equation 2dsinθ=nλ

    In the Bragg's Law, what is the equation 2dsinθ = nλ actually used to find?
  24. M

    How do waves interfere in Bragg's Law?

    I am aware that when an X ray is 'reflected' from the sheets of a crystal lattice, some radiation passes through whilst remaining radiation penetrates different layers or is scattered. And that if the path difference of the wave traveled is an integral value of wavelengths, constructive...
  25. F

    Crystal diffraction using Bragg's Law

    Homework Statement You wish to study a material with a cubic crystal structure with three orthogonal sides of length a = 0.3nm. What is the longest possible wavelength of the X-ray source you could use to reveal the (211) Bragg peak of the crystal? Homework Equations nλ =...
  26. 1

    Crystal spacing of a solid surface, Bragg's law

    Homework Statement In a particular Low Energy Electron Diffraction (LEED) study of a solid surface, electrons at 45 eV were diffracted at \phi = 53 degrees. Calculate the crystal spacing d. Homework Equations n\lambda=2dsin(\phi) \lambda = hc/E wavelength = c/v E = vh(n + 1/2) Note here v...
  27. M

    Understanding Bragg's Law in X-Ray Diffraction

    We all know, Bragg's law , n\lambda=2dsin\theta where 2dsin\theta=path difference. In the derivation of the path difference we take the two incident rays to be parallel which is perfect BUT we take reflected rays also to be parallel.How can this be since the reflected rays have to MEET for...
  28. H

    Is Bragg's Law Equation Modified for Different Incidence Angles?

    problem: In Bragg's law equation, mormally, we measure the angle θ from the surface If instead the light strikes the grating at an angle of incident θ’ (measured from the normal), show that the condition for an intensity maximum is not 2dsin θ= mλ (m=1,2,3...) but rather d(sin θ + sin θ’ ) =...
  29. K

    X-ray Diffraction and Bragg's Law

    Homework Statement On a crystal (cubic) a set of diffraction lines (θ) was obtained with CuKα (1.54 Å) radiation: 13.70, 15.89, 22.75, 26.91, 28.25, 33.15, 36.62, 37.60 and 41.95 degrees. Using the following table to determine which peaks are expected to be absent in a cubic P-, I-, and...
  30. U

    Bragg's law and double-slit experiment

    I am asked to construct a double-slit experiment for 5eV electrons. The first minimum of the diffraction pattern needs to occur at 5 degrees, what must the separation of slits be? I'm guessing that I should use Bragg's law but I don't know how to calcualte a minumum because bragg's law is for...
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