Verified Solution • 2025–26 Session moderate

QPages 383-384: Q2: HC Verma: Concepts of Physics - Volume 2 Bohr's Model and Physics of the Atom Pages 383-384: Q2 Solution: An electron with kinetic energy 5 eV is incident on a hydrogen…

⚠️ Common Exam Traps & Conceptual Pitfalls

Students often incorrectly assume that if the incident energy is below the first excitation potential (10.2 eV), the collision must be elastic. You must recognize that 'completely inelastic' in this context refers to the maximum possible kinetic energy transfer to the atom's center of mass, which is always possible regardless of internal excitation thresholds.

An electron with kinetic energy 5 eV is incident on a hydrogen atom in its ground state. The collision

Multiple Choice Options

  • A must be elastic
  • B may be partially elastic
  • C must be completely inelastic
  • D may be completely inelastic

Step-by-Step Verified Solution

**Answer:** (d) may be completely inelastic. **Step-by-Step Explanation:** The electron has 5 eV kinetic energy, which is less than the 10.2 eV needed for excitation. The collision may be elastic or completely inelastic (if the electron transfers all its energy to the atom's kinetic energy).

All Questions in this Chapter

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