An electron having kinetic energy 12.5 eV collides with a hydrogen atom initially in its ground state. Neglect the very small recoil energy of the hydrogen atom. Which collision outcomes are energetically possible?
Select all that apply

Question

An electron having kinetic energy 12.5 eV collides with a hydrogen atom initially in its ground state. Neglect the very small recoil energy of the hydrogen atom. Which collision outcomes are energetically possible?

Select all that apply

G1 Physics · Accepted Answer

Elastic scattering is energetically possible because no internal excitation energy is required. For hydrogen, Eₙ = −13.6 ÷ n² eV. Excitation to the second orbit requires ΔE₂ = 13.6[1−1 ÷ 2²] = 10.2 eV. So it is possible. Excitation to the third orbit requires ΔE₃ = 13.6[1−1 ÷ 3²] ≈ 12.09 eV. So it is also possible. Ionisation requires 13.6 eV, which exceeds 12.5 eV. Therefore A, B and C are correct.