The physics of the very small. Photons and the photoelectric effect, wave-particle duality, the quantized energy levels of atoms, and the structure, decay, and reactions of the atomic nucleus — the final unit on the AP Physics 2 exam.
Six ways to master Unit 7 — pick whichever fits how you like to study.
Eight topics from the College Board CED, in order.
Unit 7 closes out AP Physics 2 by breaking down the classical, continuous picture of energy and matter that dominates the rest of the course. You'll learn that light delivers energy in discrete packets called photons (E = hf), that matter itself can behave like a wave (the de Broglie wavelength), and that atoms can only exist in specific, quantized energy levels — explaining the discrete lines seen in atomic spectra.
The unit finishes with nuclear physics: the structure of the nucleus, Einstein's famous mass-energy equivalence, radioactive decay and half-life, and the fission and fusion reactions that power nuclear reactors and stars. This unit makes up roughly 12–15% of the AP Physics 2 exam.
Note: the College Board's revised Course and Exam Description numbers the AP Physics 2 units 9–15, continuing from AP Physics 1's units 1–8 — so this unit appears there as Unit 15: Modern Physics, with topics 15.1–15.8. We number it Unit 7 since it's the seventh and final unit of the Physics 2 course.