SAT / PSAT
SAT / PSAT Prep
History & Social Science
AP World History AP US History AP European History AP Human Geography AP US Government & Politics AP Psychology AP Macroeconomics AP Microeconomics
English
AP English Language & Composition AP English Literature & Composition
Math & Computer Science
AP Calculus AB/BC AP Precalculus AP Statistics AP Computer Science A AP Computer Science Principles
Sciences
AP Biology AP Chemistry AP Environmental Science AP Physics 1 AP Physics 2
World Languages & Arts
AP Spanish Language AP Art History AP Music Theory Start studying →
Unit 3 · Electric Circuits Flashcards Cheat Sheet Essentials Visual Review MC Practice FRQ Practice

AP Physics 2 Unit 3 Visual Review

A topic-by-topic visual walkthrough of Unit 3: Electric Circuits — current, resistance and Ohm's law, power, compound circuits, Kirchhoff's rules, and RC circuits.

← Back to Unit 3 hub
TOPIC 3.1 Electric Current Rate of charge flow I = ΔQ / Δt Unit: ampere (A) = 1 coulomb/second. CONVENTIONAL current flows in the direction a + charge would move — opposite to electron flow. conventional current I charge carriers drifting through a wire A complete loop is required Current only flows in a closed circuit driven by an EMF source (battery). Break the loop → current stops. I = ΔQ/Δt (amperes); conventional current = direction + charge moves. The Review Hub · AP Physics 2 · Unit 3 TOPIC 3.2 Simple Circuits a simple single-loop circuit +− battery (EMF) R I The components BATTERY (EMF) pushes charge around loop. WIRES carry current (≈ no resistance). RESISTOR dissipates energy as heat/light. SWITCH opens/closes the loop. Ammeter in series; voltmeter in parallel. Ohm's law ties it together V = I R A battery drives current I through resistors in a closed loop, obeying V = IR. The Review Hub · AP Physics 2 · Unit 3 TOPIC 3.3 Resistance, Resistivity & Ohm's Law Ohm's Law V = I R R = resistance (ohms, Ω). At fixed V, more resistance → less current. Ohmic materials: V–I graph is a straight line (constant R = slope). Resistivity: geometry & material R = ρ L / A ρ = resistivity (material property). Longer wire (L↑) → more R. Thicker wire (A↑) → less R. ρ usually rises with temperature. Water-pipe analogy Voltage is like pressure, current like flow rate, resistance like a narrow pipe restricting the flow. V = IR; R = ρL/A — longer & thinner wires resist more. The Review Hub · AP Physics 2 · Unit 3 TOPIC 3.4 Electric Power P = I V = I² R = V² / R Rate of energy use Power P is energy per second, in watts (W = J/s). A resistor turns electrical energy into heat and light. Energy: E = P·t Worked example A 12 V battery drives 2 A through a bulb: P = IV = (2)(12) = 24 W Its resistance: R = V/I = 12/2 = 6 Ω Check: P = V²/R = 144/6 = 24 W ✓ P = IV = I²R = V²/R (watts); a resistor dissipates energy as heat. The Review Hub · AP Physics 2 · Unit 3 TOPIC 3.5 Compound (DC) Circuits Series One path. Same current everywhere. R_eq = R₁ + R₂ + … voltages add: V = V₁ + V₂ Parallel Multiple paths. Same voltage across each. 1/R_eq = 1/R₁ + 1/R₂ + … currents add: I = I₁ + I₂ R_eq is SMALLER than the smallest resistor. Worked example Two 6 Ω resistors, 12 V battery: In SERIES: R_eq = 12 Ω → I = 1 A In PARALLEL: R_eq = 3 Ω → I = 4 A Parallel draws MORE total current because R_eq is lower. Reduce networks step by step. Series: R_eq = ΣR (same I). Parallel: 1/R_eq = Σ1/R (same V). The Review Hub · AP Physics 2 · Unit 3 TOPIC 3.6 Kirchhoff's Loop Rule Σ ΔV = 0 around any closed loop conservation of ENERGY How to apply it Walk around a loop and add up voltage changes: they return to zero. + across a battery (− to +). − IR across a resistor (with the current). Energy gained at the source = energy dropped. Worked example Single loop: 9 V battery, R₁ = 2 Ω, R₂ = 1 Ω in series. 9 − I(2) − I(1) = 0 → I = 3 A Drops: 6 V + 3 V = 9 V = EMF ✓ Loop rule: ΣΔV = 0 around any loop — energy conservation. The Review Hub · AP Physics 2 · Unit 3 TOPIC 3.7 Kirchhoff's Junction Rule Σ I_in = Σ I_out at every junction conservation of CHARGE I = 5A I₁ = 3A I₂ = 2A Charge splits, never disappears Current into a node equals current out: 5 A = 3 A + 2 A ✓ Use the junction rule for the currents and the loop rule for the voltages — together they solve any DC network. Junction rule: ΣI_in = ΣI_out — charge conservation. The Review Hub · AP Physics 2 · Unit 3 TOPIC 3.8 Resistor–Capacitor (RC) Circuits capacitor charging curve Q_max charge Q vs. time t Qt Charging & discharging over time A capacitor charges/discharges gradually through a resistor — not instantly. time constant τ = R C After one τ, ~63% charged; larger RC = slower response. Steady state (fully charged): NO current flows through the capacitor branch — it acts like an open switch. ⏱Capacitors charge over time τ = RC; fully charged → no current, acts open. The Review Hub · AP Physics 2 · Unit 3
1 / 8

How to use the visual review

Spend 30 seconds per slide before clicking next. Look at the diagram, then ask yourself: "Could I draw this from memory and explain it?"

Use the fullscreen button () on desktop for the best experience. Use arrow keys to navigate. Tap "Show all slides" to jump around.

This is great for review the night before the exam — fast, visual, and covers everything you need to remember about Unit 3's electric circuits.