College Board-Aligned Original Notes
AP Physics 2: Algebra-Based Unit 11 Topic 1: Definition and conservation of electric charge
Circuit analysis depends on the conservation of electric charge as charge moves through connected paths.
Unit 11: Electric Circuits. College Board exam weighting listed for this unit: 15%-18% of exam score.
What to Know
- Current measures the rate of charge flow past a point.
- Charge does not get used up in a circuit element.
- At a junction, charge entering per time equals charge leaving per time.
- Always connect this topic back to the larger unit: Electric Circuits.
Detailed Notes
Definition and conservation of electric charge belongs to Unit 11: Electric Circuits. Circuit analysis depends on the conservation of electric charge as charge moves through connected paths. Start by identifying the system, the field or interaction involved, and which conservation law or model applies.
Key relationships: Current measures the rate of charge flow past a point. Charge does not get used up in a circuit element. At a junction, charge entering per time equals charge leaving per time.
Model to use: Represent a junction with incoming and outgoing currents and apply charge conservation. A clear AP Physics 2 model should label directions, signs, units, and the physical meaning of each variable.
AP-style move: When currents split, use conservation of charge rather than assuming all branches have the same current. For free-response work, show the governing principle first, then connect the mathematical result back to the physical situation.
Key Vocabulary
Electric current
Rate at which electric charge flows past a point.
Conventional current
The direction positive charge would move in a circuit.
Circuit junction
A point where three or more conducting paths meet.
Charge continuity
The requirement that charge flow is conserved in a circuit.
Steady-state current
Current that remains constant with time in a circuit branch.
Quick Practice
How would you explain Definition and conservation of electric charge 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
- Resistivity and resistance
- 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.