where the symbols have their usual meanings. 

Here, \(E=15\, \mathrm{keV}=15 \times 10^{3}\, \mathrm{V}\)

and \(h c=1240\) \(eV \,nm\) 

\(\therefore \quad \lambda=\frac{1240 \,\mathrm{eV} \,\mathrm{nm}}{15 \times 10^{3} \,\mathrm{eV}}=0.083\, \mathrm{nm}\)

As the wavelength range of \(X\) -rays is from \(1\, \mathrm{nm}\) to \(10^{-3} \,\mathrm{nm},\) so this wavelength belongs to \(X-\) rays.