Particles & Radiation — A-Level Physics Revision

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What is Particles & Radiation?

This topic delves into the fundamental building blocks of the universe, introducing the Standard Model of particle physics. It explores the two main groups of fundamental particles, quarks and leptons, and the forces that govern their interactions through exchange particles. You will also study the dual nature of light, understanding it as both a wave and a particle (a photon), and investigate the photoelectric effect as key evidence for its quantum nature.

Board notes: All A-Level boards (AQA, Edexcel, OCR) cover the core concepts of the Standard Model and the photoelectric effect. The range of specific particles and decay modes required, particularly for mesons and baryons, can differ slightly. AQA typically requires the most extensive knowledge of particle properties.

Worked example

Common mistakes

• 1Confusing baryons and mesons. Students often forget that both are hadrons, but baryons (like protons) are made of three quarks, while mesons are made of a quark-antiquark pair.
• 2Misinterpreting Feynman diagrams. A common error is to draw arrows for neutral particles or to get the direction of antiparticles wrong (arrows point backwards in time).
• 3Forgetting that the kinetic energy of a photoelectron is the *maximum* possible value. The work function is the minimum energy required to release an electron, so many electrons will be released with less kinetic energy.

Particles & Radiation exam questions

Exam-style questions for Particles & Radiation with mark-scheme style solutions and timing practice. Aligned to AQA, Edexcel and OCR specifications.

Frequently asked questions

• What is the difference between a hadron and a lepton?

  Hadrons (like protons and neutrons) are particles that feel the strong nuclear force and are made of quarks. Leptons (like electrons and neutrinos) are fundamental particles that do not feel the strong force.

• What is annihilation in particle physics?

  Annihilation is the process that occurs when a particle collides with its corresponding antiparticle. Their mass is converted into energy in the form of two (or more) gamma-ray photons.