College Board-Aligned Original Notes
AP Physics C: Electricity and Magnetism Unit 13 Topic 2: Inductance (including LR circuits)
Inductance describes how circuits oppose changes in current through induced emf and magnetic energy storage.
Unit 13: Electromagnetic Induction. College Board exam weighting listed for this unit: 10%-20% of multiple-choice score.
What to Know
- An inductor stores energy in its magnetic field.
- Self-induced emf opposes changes in current.
- LR circuits have time-dependent current growth or decay set by inductance and resistance.
- Always connect this topic back to the larger unit: Electromagnetic Induction.
Detailed Notes
Inductance (including LR circuits) belongs to Unit 13: Electromagnetic Induction. Inductance describes how circuits oppose changes in current through induced emf and magnetic energy storage. In AP Physics C: Electricity and Magnetism, strong explanations connect diagrams, calculus relationships, fields, and energy or conservation principles.
Key relationships: An inductor stores energy in its magnetic field. Self-induced emf opposes changes in current. LR circuits have time-dependent current growth or decay set by inductance and resistance.
Model to use: Sketch current versus time for an LR circuit as the switch is closed or opened, then connect the curve to induced emf. Define signs, surfaces, loops, paths, and coordinate directions before writing equations.
AP-style move: At switching moments, reason about whether the inductor initially resists or later allows current change. Show the symbolic setup first, then interpret the result with direction, sign, units, and physical meaning.
Key Vocabulary
Inductance
A circuit property describing induced emf from changing current.
Self-induction
Induced emf in a circuit element caused by changing current in that same element.
Magnetic field energy
Energy stored in the magnetic field of an inductor.
LR time constant
The characteristic time scale for current changes in an inductor-resistor circuit.
Back emf
Induced emf that opposes a change in current.
Quick Practice
How would you explain Inductance (including LR circuits) in one or two AP-style sentences?
Name the concept, apply it to a specific example or source, and explain the reasoning that connects the evidence to your answer.
Related Topics in This Unit
- Electromagnetic induction (including Faraday’s Law and Lenz’s Law)
Official Alignment
Reference and Attribution
AP Physics C: Electricity and Magnetism concept reference: AP Physics C Electricity and Magnetism-Concise Summary Notes by IITian Academy. EduCompanion used this source as a topic checklist and conceptual reference, then rewrote the study notes in original wording.