kev = 80 kev ∴ Em - Ek 80 kem ..... (1) It is given that 10 kev energy is required to remove an electron from the M – shell, so that E0−Em = 10 kev ..... (2) From (1) and (2) we get E∞ - Ek 90 kev Since E∞ = 0 , Ek = - 90 kev . Thus 90 kev kev energy is required to knock out an electron from the kshell. Hence the minimum acceleration potential is 9 × 104 V . If power of 10−4 V