IBDP · Physics HL

Nuclear and Quantum Physics

E: Nuclear and Quantum Physics (E1–E5)

42 min readAdvanced~14 hours SL content extended to ~28 hours at HL (roughly 10% of the HL course); guaranteed MCQ presence in Paper 1 and at least one data/calculation question in Paper 2 every session

This topic is where the course stops behaving classically. Light starts arriving in lumps, matter starts diffracting like a wave, and half-lives make 'when will it decay' an unanswerable question for any single nucleus. The good news: almost every calculation collapses into one of three equations — $E = h f$ , $E = Δ m c^{2}$ , $N = N_{0} e^{- λ t}$ — and the marks you lose are nearly always unit conversions, not physics. HL adds the wavefunction, tunnelling, confined particles and (via fusion) a whole stellar-astrophysics layer on top.

Overview

Why this topic is graded so harshly

Every sub-topic here has a signature graph or equation that the IB reuses year after year: the photoelectric $K E_{ma x}$ -vs- $f$ line, the exponential decay curve, the binding-energy-per-nucleon curve, and (HL) the Hertzsprung-Russell diagram. Examiners test whether you can read physical meaning off these shapes — gradient, intercept, peak position — not just plug numbers in.

Quantum physics: light and matter both show particle AND wave behaviour depending on the experiment you run.
Radioactive decay, fission and fusion all trace back to one idea: mass converts to energy, $E = Δ m c^{2}$ .
HL bolts on three extra layers: the wavefunction/uncertainty/tunnelling picture of quantum mechanics, the Bohr model of atomic energy levels, and stellar structure/evolution.

Mind map of Nuclear and Quantum Physics centred on Nuclear & Quantum Physics.

Command terms this topic loves to weaponise

Command term	What it demands	AO	Mark-earning move
Calculate	Find a numerical answer with working shown	AO2	Full substitution with units at every line; a correct bald answer with no working can still lose method marks.
Determine	Multi-step numerical answer, often needs an intermediate quantity first	AO2/AO3	Marks are awarded for each intermediate value — write down $E_{p h o t o n}$ , $ϕ$ , etc. explicitly even if not asked for.
Estimate	Approximate/order-of-magnitude answer using assumed or rounded data	AO2	No single correct value — mark scheme accepts a range; stating your assumption earns a mark on its own.
Deduce	Reach a stated conclusion using given data plus a physics principle	AO3	Must name the principle (e.g. conservation of nucleon number) — the numeric answer alone forfeits the reasoning mark.
Outline	Brief account of a process or sequence (reactor operation, stellar evolution)	AO1	Needs named stages/components in order — a vague description scores zero.
Sketch	Approximately correct graph showing the key features	AO2	Axes need quantity AND unit; intercepts/asymptote/gradient sign must be shown even if not to scale.
Compare	State similarities AND differences (e.g. fission vs fusion)	AO3	A one-sided answer (only differences) loses marks — the term demands both.

Key point

Almost every quantitative question in this topic reduces to

E = h f

E = Δ m c^{2}

, or

N = N_{0} e^{- λ t}

. The marks that actually vanish are unit slips — eV↔J, u↔kg, nm↔m — not conceptual mistakes. Convert units first, calculate second.

Overview

Nuclear and Quantum Physics

Overview

Why this topic is graded so harshly

The shape of the chapter

Command terms this topic loves to weaponise