Question

Wavelength of the $k_{\alpha }$ characteristics X-ray of iron and potassium are $1.931\times {10}^{-8}$ cm and $3.737\times {10}^{-8}$ cm respectively The atomic number (approximately) of the element for which characteristics $k_{\alpha }$ wavelength is $2.289\times {10}^{-8}$ cm is (atomic number of iron is 26 and atomic number is potassium is 19)

• A. 24
• B. 28
• C. 41
• D. 30

Answer 1

Answer: (A)

From Moseley's Law,

$\sqrt{\frac{C}{\lambda }}=a(Z-1)=$

Thus $\sqrt{\frac{{\lambda }_{iron}}{{\lambda }_{element}}}=\frac{Z_{element}-1}{Z_{iron}-1}$

$⟹\frac{Z-1}{25}=\sqrt{\frac{1.931}{2.289}}$

$⟹Z=24$