A crystal has an atomic planar spacing of d $=2\mathrm{.}0.$ The X$-$ray wavelength used is

$\backslash$lambda $=1\mathrm{.}54.$ Determine the angle$(\backslash$theta $)$ at which the first$-$order diffraction peak will

be observed according to the Bragg$$s Law.Use:

$=\frac{h}{2}=\frac{6\mathrm{.}626{10}^{-34}Js}{2}$

Mass of an electron $=9\mathrm{.}109{10}^{-31}kg$

Mass of a proton $=1\mathrm{.}67{10}^{-27}kg$

Speed of light $=3{10}^8\frac{m}{s}$