College Board-Aligned Original Notes
AP Physics 2: Algebra-Based Unit 11 Topic 2: Resistivity and resistance
Resistance depends on both material properties and conductor geometry.
Unit 11: Electric Circuits. College Board exam weighting listed for this unit: 15%-18% of exam score.
What to Know
- Resistivity is a material property, while resistance also depends on length and cross-sectional area.
- Longer wires have greater resistance, while wider wires have lower resistance.
- Ohmic materials have a linear voltage-current relationship under constant conditions.
- Always connect this topic back to the larger unit: Electric Circuits.
Detailed Notes
Resistivity and resistance belongs to Unit 11: Electric Circuits. Resistance depends on both material properties and conductor geometry. Start by identifying the system, the field or interaction involved, and which conservation law or model applies.
Key relationships: Resistivity is a material property, while resistance also depends on length and cross-sectional area. Longer wires have greater resistance, while wider wires have lower resistance. Ohmic materials have a linear voltage-current relationship under constant conditions.
Model to use: Compare wires of different length, area, and material to rank their resistance. A clear AP Physics 2 model should label directions, signs, units, and the physical meaning of each variable.
AP-style move: Do not confuse resistivity with resistance; changing wire shape changes resistance even if material is unchanged. For free-response work, show the governing principle first, then connect the mathematical result back to the physical situation.
Key Vocabulary
Resistance
Opposition to electric current in a circuit element.
Resistivity
A material property describing how strongly the material opposes current.
Ohmic conductor
A conductor with constant resistance over a range of voltage and current.
Cross-sectional area
Area of a conductor perpendicular to current flow.
Current density
Current per unit cross-sectional area.
Quick Practice
How would you explain Resistivity 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
- Definition and conservation of electric charge
- Resistance and capacitance
- Kirchhoff’s loop rule
- Kirchhoff’s junction rule and the conservation of electric charge
Official Alignment
Reference and Attribution
AP Physics 2 concept reference: AP Physics 2: 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.