AQA A-Level Physics Paper 1, June 2025: Question 13

✅ Correct Answer: C

Evidence for particle nature: photoelectric effect

Evidence for wave nature: diffraction

💡 Key Knowledge

• Particle nature (Photons): The photoelectric effect provides conclusive evidence because electrons are emitted instantaneously by absorbing single discrete packets of energy (photons, where E = hf ). A wave model incorrectly predicts a time delay for energy to accumulate.
• Wave nature: Diffraction and interference are uniquely wave behaviours. When light spreads around obstacles or through slits and forms interference fringes, it must obey wave superposition.
• Line spectra: Emission and absorption line spectra provide evidence for discrete atomic energy levels (electrons transitioning between quantised orbits), rather than fundamental evidence of wave nature.

🧠 Exam Technique: Two-Column Elimination

Approach two-column multiple-choice questions by eliminating entire rows one column at a time:

1. Look at Column 1 (Particle nature): Diffraction is purely a wave phenomenon, so immediately eliminate B.
2. Look at Column 2 (Wave nature): The photoelectric effect is the classic particle experiment, so eliminate A. Line spectra arise from transitions between quantised energy states, not wave behaviour – eliminate D.
3. Verify: Photoelectric effect = particle; diffraction = wave. This leaves C as the unambiguous correct answer.

❌ Common Misconceptions

• Confusing the duality of light with electrons: Remember that electron diffraction proves that matter (particles) has wave properties, whereas light diffraction proves light (EM radiation) has wave properties.
• Misinterpreting line spectra: Students often choose option D thinking line spectra demonstrate wave behavior because wavelengths are observed. However, the existence of line spectra directly demonstrates quantised atomic energy levels in matter.
• Inverting the columns: Option A is the exact reverse of the correct row. Always read column headers twice!