Question

Find the closest integer wavelength value of K_α line (in picometer) in copper (Z = 29) if the wavelength of K_α = line in iron (Z = 26) is known to be equal to193 picometer.

Answer 1

By Mosely law $\frac{1}{\lambda} \propto(Z-1)^{2}$
$ \begin{array}{l} \frac{\lambda_{2}}{193}=\frac{(26-1)^{2}}{(29-1)^{2}} \\ \lambda_{2}=\frac{193 \times 25^{2}}{28^{2}} \\ \lambda_{2}=153.8 pm \simeq 154 pm \end{array} $