Stopping potentials of 24, 100, 110, 115 kV are measured for photoelectrons emitted from a certain element when it is irradiated with monochromatic X-rays. The element is used as a target in an X-ray tube. The energy of $K_α$ line is –

76 KeV

Let E_K, E_L, E_M, E_N be the binding energies of K, L, M and N shell. Let E_P be energy of incident
photon. Then

E_P – E_K = 24 KeV ... (1)

E_P – E_L = 100 KeV ... (2)

E_P – E_M = 110 KeV .... (3)

$E(K_α)$ = E_K – E_L = 100 – 24 = 76 KeV