AQA AS Level Physics Paper 2, June 2023: Question 15

✅ Correct Answer

D: W boson

During electron capture, a proton interacts with an inner-shell electron via the weak interaction, mediated by a charged W boson (specifically a W⁺ or W⁻ depending on how you write the Feynman diagram direction), which transfers charge between them.

💡 Key Knowledge

• Electron Capture Equation: p + e⁻ → n + vₑ
• The Weak Interaction: The only fundamental interaction capable of changing quark flavour and involving exchange bosons with non-zero rest mass and electric charge.
• Exchange Bosons: Photons mediate the electromagnetic force (zero mass/charge), whereas W⁺, W⁻, and Z⁰ bosons mediate the weak force.

🧠 Exam Technique

For multiple-choice questions on particle interactions, systematically eliminate non-applicable categories first:

• Mesons/Pions are hadrons, not exchange particles (gauge bosons). Eliminate A and B.
• Virtual photons mediate electromagnetic interactions (e.g., electron-proton scattering), not weak nuclear processes like beta decay or electron capture. Eliminate C.

❌ Common Errors

Students frequently confuse electromagnetic exchange particles (virtual photons) with weak interaction exchange particles (W bosons). Remember that any process involving a change of particle type (proton turning into a neutron) or neutrino involvement strictly requires a W boson.