Question

The wavelength of $K_{\alpha }$ line from an element of atomic number 41 is $\lambda$. Then the wavelength of $K_{\alpha }$ line of an element of atomic number 21 is

• A. $4\lambda$
• B. $\frac{\lambda }{4}$
• C. $3.08\lambda$
• D. $0.26\lambda$

Answer 1

The correct option is A

$4\lambda$

From Moseley's law, $\frac{{\lambda }_{21}}{{\lambda }_{41}}={\left(\frac{41-1}{21-1}\right)}^2=4\Rightarrow {\lambda }_{21}=4{\lambda }_{41}$
Hence, the correct choice is (a).