Electric potential difference (ΔV) is the change in electric potential energy per unit charge between two points, measured in volts (1 V = 1 J/C). In AP Physics 2 circuits, it's the "push" that drives current through resistors and stores energy in capacitors (Topic 4.3).
Electric potential difference is the difference in electric potential energy per unit charge between two points in an electric field. In symbols, ΔV = ΔU/q, and the unit is the volt, where 1 volt equals 1 joule per coulomb. A 9 V battery delivers 9 joules of energy for every coulomb of charge it pushes through a circuit.
The "per unit charge" part is the whole point. Potential difference describes the field and the two points, not any particular charge sitting there. That makes it a property of the circuit itself, which is why you can label every resistor and capacitor with a ΔV without ever asking how much charge is involved. In everyday circuit language, electric potential difference and voltage are the same thing. The exam uses both names, often in the same problem.
This term anchors Topic 4.3 (Resistance and Capacitance) in the circuits unit of AP Physics 2. Potential difference is the variable that ties the unit's two big relationships together. For resistors, ΔV = IR connects voltage to current and resistance. For capacitors, Q = CΔV connects voltage to stored charge, and U = ½CΔV² gives the stored energy. It's also the backbone of energy conservation in circuits. Kirchhoff's loop rule is literally the statement that potential differences around any closed loop add to zero, which is conservation of energy written per unit charge. If you can track ΔV around a circuit, you can solve almost any circuit problem the exam throws at you.
Keep studying AP Physics 2 Unit 4
Voltage (Unit 4)
Voltage is just the everyday name for electric potential difference. Same quantity, same units, same symbol ΔV. The exam switches between the two names freely, so treat them as interchangeable and don't let the wording throw you.
Resistance and Ohm's Law (Unit 4)
Ohm's law, ΔV = IR, says the potential difference across a resistor is what pushes current through it. More voltage means more current for the same resistance. Think of ΔV as the pressure difference and current as the flow it creates.
Series and Parallel Circuits (Unit 4)
Potential difference is how you tell these apart. In series, the battery's voltage gets split among the components, so the ΔVs add up to the total. In parallel, every branch gets the full potential difference because both ends of each branch connect to the same two points.
Electric Potential and Fields (Unit 3)
Circuits inherit this concept from electrostatics. In Unit 3, potential difference comes from doing work to move a charge through an electric field. A battery is just a device that maintains a fixed potential difference, so Unit 4 is Unit 3's field concepts put to work.
No released FRQ needs the full phrase "electric potential difference" to test it; it usually appears as ΔV or just "voltage." Multiple-choice questions love ranking tasks, like ordering the potential differences across resistors in a mixed series-parallel circuit, or asking what happens to ΔV across a capacitor when a switch closes. You should be able to apply ΔV = IR and Q = CΔV, use the loop rule to track voltage gains and drops around a circuit, and recognize that parallel branches share the same ΔV. On free-response questions, the points often come from justifying your answer with energy reasoning, such as explaining that the sum of potential differences around a loop must be zero because energy is conserved.
Electric potential energy (U) is the total energy a specific charge has, measured in joules. Electric potential difference (ΔV) is energy per unit charge, measured in volts. The relationship is ΔU = qΔV. A point in a circuit doesn't have potential energy on its own; it has a potential, and a charge placed there has energy. If a problem gives you a voltage and asks for energy, you need the charge to convert between them.
Electric potential difference is the change in electric potential energy per unit charge between two points, defined by ΔV = ΔU/q and measured in volts (1 V = 1 J/C).
Potential difference and voltage are the same quantity, and the AP exam uses both names interchangeably.
For resistors, ΔV = IR; for capacitors, Q = CΔV and the stored energy is U = ½CΔV².
In series circuits the potential differences across components add up to the battery's voltage, while in parallel circuits every branch gets the same potential difference.
Kirchhoff's loop rule says potential differences around any closed loop sum to zero, which is conservation of energy stated per unit charge.
ΔV is a property of two points in a circuit or field, not of any particular charge, which is why you can analyze a circuit without knowing how much charge flows.
It's the difference in electric potential energy per unit charge between two points, ΔV = ΔU/q, measured in volts. In circuits (Topic 4.3), it's the quantity that drives current through resistors and determines the charge stored on capacitors.
Yes. Voltage is just the common name for electric potential difference, and both use the symbol ΔV and the unit volts. The AP exam treats them as identical, so don't read them as two different ideas.
Potential energy (U, in joules) is the total energy of a specific charge, while potential difference (ΔV, in volts) is energy per coulomb of charge. They're linked by ΔU = qΔV, so a 2 C charge moving through 9 V gains or loses 18 J.
No, not in a resistive circuit. Ohm's law (ΔV = IR) means zero potential difference across a resistor gives zero current through it. This is also why an ideal wire, which has essentially zero resistance, can carry current with almost no voltage drop across it.
Because both ends of every parallel branch connect to the same two points in the circuit, and ΔV is defined between two points. Each branch sees the full potential difference, while the current splits among the branches based on their resistances.