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 –
Answer & explanation
Correct answer: option 2
Let EK, EL, EM, EN be the binding energies of K, L, M and N shell. Let EP be energy of incident
photon. Then
EP – EK = 24 KeV ... (1)
EP – EL = 100 KeV ... (2)
EP – EM = 110 KeV .... (3)
$E(K_α)$ = EK – EL = 100 – 24 = 76 KeV