College Board-Aligned Original Notes
AP Physics C: Electricity and Magnetism Unit 11 Topic 1: Current and resistance
Current describes charge flow, while resistance describes how a circuit element opposes that flow.
Unit 11: Electric Circuits. College Board exam weighting listed for this unit: 15%-25% of multiple-choice score.
What to Know
- Current is charge per time through a cross section.
- Resistance depends on resistivity, length, and cross-sectional area.
- Microscopic current models connect drift velocity, charge carrier density, charge, and area.
- Always connect this topic back to the larger unit: Electric Circuits.
Detailed Notes
Current and resistance belongs to Unit 11: Electric Circuits. Current describes charge flow, while resistance describes how a circuit element opposes that flow. In AP Physics C: Electricity and Magnetism, strong explanations connect diagrams, calculus relationships, fields, and energy or conservation principles.
Key relationships: Current is charge per time through a cross section. Resistance depends on resistivity, length, and cross-sectional area. Microscopic current models connect drift velocity, charge carrier density, charge, and area.
Model to use: Use a conductor model with moving charge carriers and relate microscopic motion to macroscopic current. Define signs, surfaces, loops, paths, and coordinate directions before writing equations.
AP-style move: Distinguish current direction from electron drift direction in metallic conductors. Show the symbolic setup first, then interpret the result with direction, sign, units, and physical meaning.
Key Vocabulary
Electric current
Rate of charge flow through a surface.
Resistance
Opposition to current through a conductor or circuit element.
Resistivity
A material property that affects resistance.
Drift velocity
Average velocity of charge carriers through a conductor.
Charge carrier density
Number of mobile charge carriers per unit volume.
Quick Practice
How would you explain Current and resistance 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
- Current, resistance, and power
- Steady-state direct-current circuits with batteries and resistors only
- Gauss’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.