The wavelength of `K_(alpha)` X-ray for an element is 21.3 pm. It takes 12.5 ke V to knock out an electron out an electron from the L-shell of the atom of the element. What should be the minimum accelerating voltage across on X-ray tube having the element as target which allows production of `K_(alpha)` X-ray?

Explanation

Since `E_(K)-E_(L)=(hc)/(lambda_(K_(alpha)))`
It is given that `lambda_(K_(alpha))=21.3"pm" =0.0213 "nm"`
Also, `" " E(eV) =(1242)/(lambda(nm))=(1242)/(0.0213)=58.3 eV`
`rArr" " E_(K)-E_(L)=E`
`rArr" " E_(K)-12.5=58.3`
`rArr" "E_(K)=70.8 keV`
`:.` Acceleration potential =70.8 keV