If the Kα radiation of Mo (Z = 42) has a wavelength of 0.71 Å the wavelength of the corresponding radiation of Cu (Z = 29)
1 Å
2 Å
1.52 Å
1.25 Å
Moseley's law
For Kα , λ ∝ 1Z-12
λ2λ1=Z1-12Z2-12 ⇒λ20.71=(42-1)2(29-1)2 ⇒λ2=1.522A˙