Question

At what angles for the first order diffraction, spacing between two planes, respectively, are $\lambda$ and $\frac{\lambda }{2}$?

• A. $0^{\circ },{90}^{\circ }$
• B. ${90}^{\circ },0^{\circ }$
• C. ${30}^{\circ },{90}^{\circ }$
• D. ${90}^{\circ },{30}^{\circ }$

Answer 1

The correct option is C ${30}^{\circ },{90}^{\circ }$

We know the Bragg's equation is given by $n\lambda =2dsin\theta$.

First order diffraction: $n=1$ and $d=\lambda$
$⟹\theta ={30}^o$
First order diffraction: $n=1$ and $d=\frac{\lambda }{2}$
$⟹\theta ={90}^o$