Stopping potential of 24, 100, 110 and 115 k V are measured for photoelectrons emitted from a certain element when it is radiated with monochromatic X-ray . If this element is used as a target in an X-ray tube,what will be the wavelength of `K_a` - line?

Answer

A, C

Explanation

Stopping potentials are 24, 100, 110 and 115 kV, i.e. if the electrons are emitted from conduction band maximum kinetic energy of photoelectrons would be `115xx10^3` eV. If they are emitted from next inner shell, maximum kinetic energy of photoelectrons would be `110xx10^3 eV` and so on. for photoelectrons of L- shell it would be `100xx10^3` eV and for K- shell it is`24xx10^3` ev. Therefore, diference between energy of L-shell and K-shell is
`Delta E = E_L - K_K`
`=(100 - 24)xx10^3 eV`
`= 76xx10^3`eV
`:.` Wavelength of `K_a` line (transition of electron form L-shell to K-shell) is,
`lambda_(ka) (in Å) = (12375)/(DeltaE(in eV) = (12375)/(76xx10^3)`
`= 0.163 Å`.