question_answer

A beam of monoenergetic photons of energy \[\mathbf{9}\text{ }\mathbf{eV}\] is incident on a hydrogen gas containing all atoms in ground state. It is found that the beam is fully transmitted without absorption. Why?           

Answer:

                A hydrogen atom in ground state can absorb a minimum energy of \[{{E}_{2}}-{{E}_{1}}=-3.4-(-13.6)=10.2eV\] So, photons of energy \[\text{9 eV}\] cannot be absorbed by hydrogen atoms in ground state.