How light bounces and bends. Reflection off mirrors, refraction through different media, Snell's law, total internal reflection, and how mirrors and lenses form images — all explained by tracing simple geometric rays of light.
Six ways to master Unit 5 — pick whichever fits how you like to study.
Four topics from the College Board CED, in order.
Unit 5 treats light as rays traveling in straight lines, bouncing off surfaces (reflection) and bending as they cross between materials (refraction). You'll learn the simple, elegant law of reflection and the more nuanced Snell's law, which together explain everything from how a flat mirror works to why a straw looks bent in a glass of water.
The unit builds toward image formation in mirrors and lenses — using both algebraic equations and geometric ray diagrams to predict where an image will appear, whether it's upright or inverted, and whether it's real (can be projected on a screen) or virtual (only visible by looking into the optical device). 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 13: Geometric Optics, with topics 13.1–13.4. We number it Unit 5 since it's the fifth unit of the Physics 2 course.