This HL-only mini-lesson covers Theme E.2 — Quantum physics: the photoelectric effect and photons, wave–particle duality, the de Broglie wavelength and matter waves, and atomic energy levels.
Work through each screen, answer the questions as you go (some are reasoning, some are calculations) and collect ⭐ stars. Watch for the HL flag on higher-level extensions. Press Start when you're ready.
Light comes in quanta called photons, each carrying energy proportional to frequency. Shining light on a metal can eject electrons (the photoelectric effect) — but only if the frequency exceeds a threshold set by the work function φ:
Increasing the intensity below the threshold frequency still ejects NO electrons — a fatal problem for the wave model and the evidence that light is quantised.
If waves can act as particles, particles can act as waves. Every moving particle has a de Broglie wavelength:
The wavelength is tiny for everyday objects (huge momentum), which is why we never see a cricket ball diffract — but it is measurable for electrons.
Electrons in atoms occupy discrete energy levels. When an electron drops from a higher level E₂ to a lower E₁, a photon is emitted whose frequency is fixed by the energy gap:
Because the levels are quantised, only specific photon energies appear — the "barcode" line spectrum that identifies each element.
Tap an item, then tap the group it belongs to.
Tap a statement on the left, then its match on the right.
Photons: E = hf; light is quantised
Photoelectric: hf = φ + E_max; needs f above threshold, not just intensity
Duality: λ = h/p; particles diffract like waves
Energy levels: discrete; hf = E₂ − E₁ gives line spectra
Evidence: photoelectric = particle nature of light; diffraction = wave nature of matter
That completes Quantum Physics for IB Diploma Physics HL. Press Finish to see your score.
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