Minimum excitation energy will be difference between ground level energy (n=1) and first excited state (n=2). For hydrogen atom, energy in ground state, E1=−13.6eV Energy in first excited state, E2=−
136
22
=−
13.6
4
=−34eV Energy required for excitation, ∆E=E2−E1 =−34−(−136) =10.2eV ∴ Excitation potential, =