Question

Derive bragg's equation of x-ray diffraction. Explain the uses of this equation in crystallography.

Answer 1

Bragg's Law can easily be derived by considering the conditions necessary to make the phases of the beams coincide when the incident angle equals and reflecting angle. The rays of the incident beam are always in phase and parallel up to the point at which the top beam strikes the top layer at atom z (Fig. 1). The second beam continues to the next layer where it is scattered by atom B. The second beam must travel the extra distance AB + BC if the two beams are to continue traveling adjacent and parallel. This extra distance must be an integral (n) multiple of the wavelength (lambda) for the phases of the two beams to be the same:

(eq 2) nlambda = AB +BC .