Problem
Problem
Electrons with energy 80 keV are incident on the tungsten target of an X-ray tube. K-shell electrons of tungsten have 72.5 keV energy. X-rays emitted by the tube contain only (JEE 2000) a. a continuous X-ray spectrum (Bremsstrahlung) with a minimum wavelength of b. a continuous X-ray spectrum (Bremsstrahlung) with all wavelengths c. the characteristic X-ray spectrum of tungsten d. a continuous X-ray spectrum (Bremsstrahlung) with a minimum wavelength of and the characteristic X-ray spectrum of tungstenIntuitive explanation
When a high-energy electron knocks a K-shell electron out of tungsten, an outer electron falls down to fill the vacancy, releasing energy as an X-ray. The key insight is that the X-ray energy equals the energy difference between two electron shells—but you're limited by what transitions are actually possible. Since incident electrons have 80 keV and K-shell electrons need 72.5 keV to remove, you can create K-shell vacancies, allowing L→K, M→K, and higher transitions. However, you cannot create vacancies in shells deeper than K with these incident energies, so certain X-ray lines simply won't appear.
Intuitive explanation
When a high-energy electron knocks a K-shell electron out of tungsten, an outer electron falls down to fill the vacancy, releasing energy as an X-ray. The key insight is that the X-ray energy equals the energy difference between two electron shells—but you're limited by what transitions are actually possible. Since incident electrons have 80 keV and K-shell electrons need 72.5 keV to remove, you can create K-shell vacancies, allowing L→K, M→K, and higher transitions. However, you cannot create vacancies in shells deeper than K with these incident energies, so certain X-ray lines simply won't appear.