Question

A hydrogen atom having kinetic energy $E$ collides with a stationary hydrogen atom. Assume all motions are taking place along the line of motion of the moving hydrogen atom. For this situation, mark out the correct statement(s)

• A. For $E\ge 20.4eV$ only, collision would be elastic
• B. For $E\ge 20.4eV$ only, collision would be inelastic
• C. For $E=2.4eV$, collision would be perfectly inelastic
• D. For $E=18eV$, the $KE$ of initially moving hydrogen atom after collision is zero

Answer 1

Answer: (B), (D)

The correct options are
B For $E\ge 20.4eV$ only, collision would be inelastic
D For $E=18eV$, the $KE$ of initially moving hydrogen atom after collision is zero

K.E=2P.E
For electron in hydrogen to excite, a minimum of 10.2eV energy is required. Therefore, minimum 20.4eV K.E is required for inelastic collision otherwise, electron would not accept energy. And if E=20.4eV, collision would be perfectly inelastic.
If E is less than 20.4eV, collision is elastic and the two hydrogen atoms exchange velocities.
Therefore, B,D are the correct answers.