Question
Find the maximum potential difference which may be applied across an X-ray tube with tungsten target without emitting any characteristic K or L X-ray. The energy levels of the tungsten atom with an electron knocked out are as follows.
Cell containing vacancy
K
L
M
Energy in keV
69.5
11.3
2.3

Answer

Let for, k series emission the potential required = v
$\therefore$ Energy of electrons = ev
This amount of energy ev = energy of L shell
The maximum potential difference that can be applied without emitting any electron is 11.3ev.

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