The physics of charges in motion. Current and resistance, Ohm's law, series and parallel circuits, Kirchhoff's rules for multi-loop circuits, and how capacitors behave when wired into a circuit — including the time-dependent behavior of RC circuits.
Six ways to master Unit 3 — pick whichever fits how you like to study.
Eight topics from the College Board CED, in order.
Unit 3 takes the electrostatics tools from Unit 2 and puts them to work in moving circuits. You'll learn how current is just charge in motion, how Ohm's law connects voltage, current, and resistance, and how to analyze circuits of growing complexity — from simple series and parallel combinations up through multi-loop circuits that require Kirchhoff's rules.
This unit ties with Units 1 and 2 as the highest-weighted unit on the exam at roughly 15–18% of the AP Physics 2 exam. Circuit analysis is one of the most heavily tested skills on the free-response section, so this unit rewards careful, consistent practice.
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 11: Electric Circuits, with topics 11.1–11.8. We number it Unit 3 since it's the third unit of the Physics 2 course.