Question

Frequencies of Kα X-rays of different materials are measured. Which one of the graphs in the figure may represent the relation between the frequency v and the atomic number Z ?

Answer 1

Using Moseley's Law,

${\displaystyle \sqrt{v}=a(Z-b)}$,

where v = frequency of K_α X-ray
            Z = atomic number

${\displaystyle \therefore v=a^2{(Z-b)}^2}$

⇒ ${\displaystyle {(Z-b)}^2=\frac{v}{a^2}}$

This is  the equation of a parabola with some intercept on the axis, representing atomic number (Z). Hence, curve d represent this relation correctly.