X-Ray Study of Crystal Structure
Study of internal structure of crystal can be done with the help of X-rays. The distance of the constituent particles can be determined from diffraction value by Bragg’s equation.
Where, l = Wave length of X-rays, n = order of reflection, 
Angle of reflection, d = Distance between two parallel surfaces
The above equation is known as Bragg’s equation or Bragg’s law. The reflection corresponding to n = 1 (for a given family of planes) is called first order reflection; the reflection corresponding to n = 2 is the second order reflection and so on. Thus by measuring n (the order of reflection of the X-rays) and the incidence angle q, we can know d/l.
From this, d can be calculated if l is known and vice versa. In X-ray reflections, n is generally set as equal to 1. Thus Bragg’s equation may alternatively be written as
= 2 dhkl sinq
Where dhkl denotes the perpendicular distance between adjacent planes with the indices hkl.