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Cambridge International AS & A Level - particles

A-Level Physics particle physics

Particle physics is an evidence map across scales. Organize the named particles by structure and interaction, connect conservation laws to allowed processes, and keep experimental observations separate from the models used to explain them.

Framework
Cambridge Physics 9702
Level
Cambridge International AS & A Level Physics
Guide format
Particle and nuclear physics guide

Start with the model

Classify first; apply conservation second.

Atoms contain nuclei and electrons; nuclei contain protons and neutrons; nucleons are composite particles described in terms of quarks. Leptons are not built from quarks in the model used here. A classification table should record charge, family, antiparticle, and the interactions relevant to the process being studied.

Reaction and decay equations are constrained by conservation laws. Check charge and nucleon-related quantities across the entire process, then connect the symbolic equation to evidence such as tracks, energy spectra, scattering, or detector counts. Radioactive decay is statistical for an individual nucleus but predictable for a large population.

Study pathway

Four decisions that organize the topic.

Follow the sequence or open the step that matches your current gap. Destination pages keep their existing access rules.

  1. 01

    Build the particle family tree

    Separate leptons from hadrons and baryons from mesons, then connect composite particles to quark content.

    Open this step
  2. 02

    Balance interactions

    Use conservation checks to decide whether a proposed reaction or decay is physically allowed in the course model.

    Open this step
  3. 03

    Connect photons to evidence

    Relate photon energy and momentum to the photoelectric effect, spectra, and quantized energy changes.

    Open this step
  4. 04

    Model nuclear change

    Distinguish activity, decay probability, half-life, binding energy, fission, and fusion.

    Open this step

Use it deliberately

A particle-process ledger

Turn every reaction, decay, or detector story into a ledger before calculating energy or momentum.

  1. 01

    List every initial and final particle with charge, family, and any composite structure needed for the question.

  2. 02

    Check conserved quantities across the whole process before accepting a proposed equation.

  3. 03

    Distinguish rest energy, kinetic energy, photon energy, and binding-energy change in the energy account.

  4. 04

    State what observation supports the model and what the observation alone does not prove.

Continue on GioPhysics

A mapped route, not a search-results wall.

Curriculum context on this page is public. Lessons, presentations, files, and practice follow the access message shown when you open them.

MapAtomic, nuclear, and quantum directorySee particle, quantum, and nuclear concepts in their syllabus placement.ClassifyThe Standard ModelOrganize particles, antiparticles, families, and interactions.ObserveThe photoelectric effectConnect photon energy to threshold evidence and electron emission.DecayRadioactivityModel nuclear radiation, decay equations, activity, and half-life.PractiseParticle applicationsApply Standard Model, decay, and nuclear reasoning in graduated problems.

Questions before you begin

Clear scope, honest expectations.

What is the simplest way to organize particle families?

Start with leptons and hadrons. Split hadrons into baryons and mesons, then record quark composition, charge, and antiparticle relationships where the course requires them.

How do I check a particle reaction?

Write a ledger for the initial and final sides and check every relevant conserved quantity. Only then calculate energy or momentum.

Is radioactive decay predictable?

The decay time of one nucleus is not predictable, but the behaviour of a large population follows a statistical law described by activity, decay constant, and half-life.