AQA A-Level Physics Paper 1, June 2022: Question 12

✅ Correct Answer: Option B

Strange particles are always created in pairs.

Because strangeness is conserved via the strong interaction (which governs particle creation in high-energy collisions), strange quarks contain a non-zero strangeness number (e.g., strange quark has S = -1 ). To conserve total strangeness from an initial state where S = 0 (ordinary matter like protons/neutrons), strange particles must be produced together (e.g., a K⁰ and a Λ baryon).

💡 Key Knowledge

• Creation vs. Decay: Strange particles are created via the strong interaction (where strangeness is conserved, ΔS = 0 ). However, they decay via the weak interaction (where strangeness can change by 0 or ±1 ).
• Baryons & Mesons: Strange particles include both mesons (like kaons, containing a strange/antistrange quark) and baryons (like the Lambda Λ or Sigma Σ baryons containing a strange quark).

🧠 Exam Technique

Read through every option carefully before committing. In multiple-choice questions, eliminate statements containing absolute limitations unless they are fundamental laws (e.g., words like "only" or "always" should make you hyper-vigilant).

❌ Common Errors & Distractors

• Option A: Incorrect because strange particles can also be baryons (e.g., the Lambda baryon Λ ), not just mesons.
• Option C: Incorrect because strangeness is conserved (does not change) in strong interactions. It is the weak interaction where strangeness can change.
• Option D: Incorrect because strangeness can take other integer values such as +1 , +2 , or -2 depending on the quark composition (e.g., the Xi baryon contains two strange quarks and has S = -2 ).