For a second diffraction using X-ray Bragg's equation, for a crystal with separation between two layers as d $\stackrel{\mathrm{o}}{\mathrm{A}}$, following graphical study was observed when varying $\theta$ at different $\lambda$.

What is the value of d?

By using Bragg's equation,

$\mathrm{n}\lambda =2\mathrm{dsin}\theta \text{ where, }\mathrm{n}=2\text{ (2nd diffraction) }$

$\lambda =\mathrm{dsin}\theta \text{ or }\log \lambda =\log \mathrm{d}+\log \sin \theta$

d is constant (distance between two planes) as $\theta$ changes, $\lambda$ also changes.

When $\theta$ = 90°, sin = 90° = 1, hence log sin 90° = 0

OX = 0.3010 $\stackrel{\mathrm{o}}{\mathrm{A}}$

$\therefore$ log $\lambda$ = 03012 $\stackrel{\mathrm{o}}{\mathrm{A}}$ $\therefore$ $\lambda$ = 2.0 $\stackrel{\mathrm{o}}{\mathrm{A}}$