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,
$\sqrt{v}=a\left(Z-b\right)$,
where v = frequency of K_α X-ray
Z = atomic number

$$\begin{gathered} \therefore v=a^2{\left(Z-b\right)}^2 \\ \Rightarrow {\left(Z-b\right)}^2=\frac{v}{a^2} \end{gathered}$$
This is the equation of a parabola with some intercept on the axis, representing atomic number (Z). Hence, curve d represent this relation correctly.