Question

Calculate the wavelength of $k_{\alpha }$ line for $Z=31$ when $\alpha =5\times {10}^7{Hz}^{1/2}$ for a characteristic X-ray spectrum.

• A. $1.33\stackrel{\circ }{A}$
• B. $1.33nm$
• C. $133\times {10}^{-10}m$
• D. $133nm$

Answer 1

The correct option is A $1.33\stackrel{\circ }{A}$

Given, $\alpha ={5\times 10}^7{Hz}^{1/2}$

From Moseley's Law,

$\sqrt{f}=\alpha (Z-k_2)$

$k_2=1$ for $\alpha$-line

$\therefore f={\alpha }^2(Z-1{)}^2$

$\lambda =c/f=\frac{3\times {10}^8}{25\times {10}^{14}\times (31-1{)}^2}$

$\lambda =1.33\times {10}^{-10}m=1.33\mathring{A}$