Electrons with energy 80 keV are incident on the tungsten target of an X-ray tube. K shell electrons of tungsten have ionization energy 72.5 keV. X-rays emitted by the tube contain only

Minimum wavelength of continuous X-ray spectrum is given by Also the energy of the incident electrons (80 KeV) is more than the ionization energy of the K-shell electrons (i.e. 72.5 KeV). Therefore characteristic X-ray spectrum will also be obtained because energy of incident electron is enough to knock out the electron from K or L shells