Atomic and Molecular Physics

JKPSC Assistant Professor (Physics) · Physics · 57 practice questions with answers and explanations: 2 Easy, 53 Medium, 2 Hard.

Sample questions

Sample Easy question 1

The Bohr radius of the hydrogen atom is about:

  1. 5.3 Å
  2. 1.06 Å
  3. 0.53 Å
  4. 0.053 Å
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Answer: C. a₀ = 4πε₀ħ² ÷ (m e²).

Sample Easy question 2

The ground-state energy of the hydrogen atom is:

  1. −13.6 eV
  2. −1.51 eV
  3. −3.4 eV
  4. −27.2 eV
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Answer: A. It is the ionisation energy of hydrogen with the sign reversed.

Sample Medium question 3

The vibrational frequency of a diatomic molecule is proportional to:

  1. √(k/μ)
  2. √(μ/k)
  3. μ/k
  4. k/μ
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Answer: A. μ is the reduced mass.

Sample Medium question 4

The vibrational energy of an anharmonic oscillator is:

  1. vħω
  2. v²ħω
  3. (v + ½)ħω
  4. (v + ½)ħω − (v + ½)²ħωx
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Answer: D. It leads to converging levels.

Sample Medium question 5

The rotational spectrum of a rigid diatomic rotor has lines that are:

  1. Equally spaced
  2. Continuous
  3. Unequally spaced
  4. Single
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Answer: A. The spacing is 2B.

Sample Hard question 6

The Lamb shift is the small energy difference between the hydrogen levels:

  1. 2P₁/₂ and 2P₃/₂
  2. 2S₁/₂ and 2P₁/₂
  3. 3D and 3P
  4. 1S and 2S
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Answer: B. It is explained by quantum electrodynamics.

Sample Hard question 7

The fine-structure constant α is approximately:

  1. 1/1837
  2. 1/273
  3. 1/137
  4. 1/12
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Answer: C. α = e² ÷ (4πε₀ħc).

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