A-Level Physics: Particle Physics

Particle physics is the most vocabulary-dense topic in the first year of A-Level Physics: a taxonomy of particles, a set of conservation laws, and a handful of rules that decide which interactions can happen. This quiz drills all three layers with the precision the multiple-choice format enforces.

The classification questions map the particle zoo: hadrons split into baryons (three quarks) and mesons (quark-antiquark), leptons standing outside the quark system, and specific quark compositions tested directly — the up-antidown content of the positive pion, and which three-quark combinations can form a baryon. Antiparticles get a dedicated question on what flips (charge and quantum numbers) and what does not (mass), extended by a strangeness question on the neutral kaon and its antiparticle.

The conservation-law questions are where exam marks concentrate. Neutron beta decay is analysed against charge, baryon number and lepton number — with the antineutrino's negative lepton number doing the balancing — with quark flavour as the instructive wrong answer, since a down quark becomes an up quark in this weak decay.

Exchange particles complete the picture: the virtual photon for electromagnetism, and which real interactions (beta-minus decay, electron capture) proceed through the weak force. A specific-charge calculation grounds the topic's one routine calculation: charge over mass for a proton-mass particle.

Every explanation names the rule being applied, building exactly the justify-your-answer reasoning that particle physics questions demand.

Classify particles into baryons, mesons and leptons and give quark compositions
State what antiparticles share with and how they differ from their particles
Apply charge, baryon number and lepton number conservation to real decays
Know that quark flavour and strangeness can change in weak interactions
Calculate specific charge and identify exchange particles per interaction

Topic scope follows the A-level physics content — as organised, for example, in section 3.2.1 (Particles) of the AQA A-level Physics (7408) specification: constituents of the atom, antiparticles, hadron and lepton classification, quark composition, conservation laws and exchange particles.

Sample question

A particle has a mass of $1.67 \times 10^{-27} \text{ kg}$ and a charge of $+1.60 \times 10^{-19} \text{ C}$. Calculate its specific charge.

$1.06 \times 10^7 \text{ C kg}^{-1}$
$9.58 \times 10^6 \text{ C kg}^{-1}$
$9.58 \times 10^7 \text{ C kg}^{-1}$
$1.06 \times 10^8 \text{ C kg}^{-1}$

See the answer

$9.58 \times 10^7 \text{ C kg}^{-1}$

Specific charge is defined as the ratio of charge to mass. Calculating $\frac{1.60 \times 10^{-19}}{1.67 \times 10^{-27}}$ yields approximately $9.58 \times 10^7 \text{ C kg}^{-1}$.

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