Q. An electron with kinetic energy $5\ eV$ is incident on a $H$-atom in its ground state. The collision
A) Must be elastic
B) May be partially elastic
C) Must be completely elastic
D) May be completely inelastic
Explanation
(a) In hydrogen atom $E_{2} - E_{1} = 10.2eV$
Since, $5eV < 10.2eV$
The electron excites the hydrogen atom. The collision must be therefore elastic
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.