Nuclear and Quantum Physics
IB Physics Guide (2023) — Theme E: Nuclear and quantum physics
Everything in this chapter comes back to one idea: energy is quantised and nuclei are held together by a balance you can calculate. Get the notation, the conservation rules, and the binding-energy curve solid, and the fission/fusion/decay questions answer themselves. The quantum sections (photoelectric effect, matter waves) are flagged HL where they go beyond the SL core, but the photon and spectra work is pure SL and shows up on Paper 1 every year.
Overview & how it connects
Theme E splits into two halves that share one tool — the photon. The nuclear half asks what holds a nucleus together and what happens when that balance breaks (decay, fission, fusion). The quantum half asks why energy comes in lumps (spectra, photons, and at HL the photoelectric effect and matter waves). The bridge between them is : the same equation explains a gamma ray from a decaying nucleus and a line in a hydrogen spectrum.
Almost every mark in this topic is won by getting three things automatic: reading and balancing nuclear equations, using the binding-energy-per-nucleon curve to predict energy release, and switching between , activity , half-life and decay constant without stalling.
The shape of the chapter
Command terms that dominate this topic
| Command term | What it demands | AO | Mark-earning move |
|---|---|---|---|
| State / Write down | Give a specific answer with no working or justification. | AO1 | One clean line — e.g. the decay equation, correctly balanced. Don't explain; you get the mark for the correct statement only. |
| Determine / Calculate | Find a number, showing the route to it. | AO2 | Substitution mark + answer mark. Write the equation, sub in with units, then the value. A bare answer risks losing the method mark if it's wrong. |
| Show that | Prove a given result — the answer is printed for you. | AO2 | Carry one more significant figure than the printed value and finish with a line like '≈ 8.8 MeV as required'. Never just restate the target. |
| Explain | Give reasons, linking cause to effect. | AO2/AO3 | Each distinct reason = a mark. For the photoelectric effect, 'photon interacts one-to-one with one electron' is the sentence markers hunt for. |
| Sketch | A shaped graph with the key features labelled — not to scale. | AO2 | Get the shape right (exponential decay curves through N₀; BE/nucleon peaking near A=56) and label both axes with quantities. |
| Estimate | A rough value using sensible assumptions. | AO2 | State the assumption you made (e.g. 'treat the nucleus as a sphere'). Order-of-magnitude is usually enough — don't over-work it. |
Key point
Overview