Answer to Question #110609 in Physical Chemistry for DEEPAK SINGH

Question

State bragg law.list the assumption made by bragg in deriving bragg equation.

Answer 1

Bragg’s law of diffraction on crystal planes states that

2d*sin$\Theta$ = n$\lambda$

where d is interplane distance, $\Theta$ is glancing angle between crystal plane and incident radiation ray, $\lambda$ is wavelength of radiation, n is integer number 1, 2, 3, etc.

The assumptions are: the ray of monochromatic radiation is incident on a crystal. The crystal is perfect and infinite. The ordered atomic structure of a crystal may be considered as a set of parallel atomic planes. The radiation from the primary ray is partially reflected by each of the atomic plane and partially transmitted through it in the forward direction. The parts of radiation reflected from the previous and the subsequent atomic planes interfere positively resulting in diffraction maxima. The condition for positive interference is that the two rays reflected from a sequence of atomic planes separated by distance d is that the difference in their path lengths (2d*sin$\Theta$) equals to inter number of wavelengths n$\lambda$