Question

The energy of a $K$-electron in tungsten is $-20keV$ and of an $L$-electrons is $-2keV$. The wavelength of X-rays emitted when there is electron jump from $L$ to $K$ shell:

• A. $0.3443\mathring{A}$
• B. $0.6887\mathring{A}$
• C. $1.3982\mathring{A}$
• D. $2.78\mathring{A}$

Answer 1

The correct option is B $0.6887\mathring{A}$

A

$E_L=-2KeV=-2\times {10}^3\times 1.6\times {10}^{-19}J$

$E_K=-20KeV=-20\times {10}^3\times 1.6\times {10}^{-19}J$

The energy of the x-ray photon is given as

$E=E_L-E_K=hv=\frac{hc}{\lambda }$

Or, $\lambda =\frac{hc}{E_L-E_K}=\frac{6.62\times {10}^{-34}\times 3\times {10}^8}{18\times {10}^{3}1.6\times {10}^{-19}}m=0.6887\dot{A}$