AQA AS Level Physics Paper 2, June 2022: Question 13

✅ Correct Answer: C (line spectra)

Line emission and absorption spectra consist of discrete frequencies (or wavelengths). Because energy is related to frequency by E = hf , the emission or absorption of specific, sharp frequencies proves that atoms make transitions between fixed, quantised energy levels.

💡 Key Knowledge

• Electrons in atoms can only occupy specific energy values called energy levels.
• When an electron transitions from a higher level to a lower level, it emits a photon with energy equal to the difference between the levels ( E₂ - E₁ = hf ).
• Because the energy differences are fixed, only specific photon frequencies are produced, resulting in a line spectrum rather than a continuous spectrum.

🧠 Exam Technique

For multiple-choice recall questions like this, mentally review the core phenomena taught in the quantum physics module before reading the options. Match keywords like "discrete frequencies" or "wavelengths" straight to line spectra.

❌ Common Errors & Distractors

• Beta-plus decay (A): Evidence for the weak nuclear force and neutrino emission, not atomic energy levels.
• Electron diffraction (B): Evidence for the wave nature of electrons (de Broglie wavelength), not atomic energy levels.
• The photoelectric effect (D): Evidence for the particulate (photon) nature of electromagnetic radiation and energy transfer in one-to-one interactions, not discrete levels inside an atom.