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A2 · Topic 22

Where physics broke and rebuilt itself.

Light arrives in photons, electrons diffract like waves, and atoms emit only certain colours. This topic covers photon energy and momentum, the photoelectric effect, wave-particle duality, and the discrete energy levels behind line spectra. Play the four simulations below. The gamified lessons and the topic Paper 4 practice are live below too.

Simulations · live
Interactive · live Energy and momentum of a photon Tune the wavelength and watch energy, frequency and momentum change together across the spectrum. Loads only when you launch, so the page stays fast.
Interactive · live The photoelectric effect Cross the threshold frequency, then change intensity to see the rate change but not the maximum energy. Loads only when you launch, so the page stays fast.
Interactive · live Electron diffraction and de Broglie Accelerate electrons and watch their de Broglie wavelength fall as the diffraction rings close in. Loads only when you launch, so the page stays fast.
Interactive · live Energy levels and line spectra Pick hydrogen transitions and read off the wavelength of each emission or absorption line. Loads only when you launch, so the page stays fast.
Paper 4 practice · live
Structured questions · with worked solutions Ten original Paper 4 style questions A full topic set across photons, the photoelectric effect, duality and energy levels, linking the lessons with full worked solutions. Open practice →
Lessons · live
Energy and momentum of a photon → The photoelectric effect → Wave-particle duality → Energy levels and line spectra →
Concept map
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