Potential difference and power
Cambridge A-Level Physics (9702) · Unit 9: Electricity · 8 flashcards
Potential difference and power is topic 9.2 in the Cambridge A-Level Physics (9702) syllabus , positioned in Unit 9 — Electricity , alongside Electric current and Resistance and resistivity. In one line: Potential difference (V) is the energy transferred per unit charge. It is the work done (W) in moving a unit charge (Q) between two points in a circuit. V = W / Q.
Marked as AS Level: examined at AS Level in Paper 1 (Multiple Choice), Paper 2 (AS Structured Questions) and Paper 3 (Advanced Practical Skills). The same content may also be assumed in Paper 4 (A Level Structured Questions).
The deck below contains 8 flashcards — 4 definitions and 4 calculations — covering the precise wording mark schemes reward. Use the 4 definition cards to lock down command-word answers (define, state), then move on to the concept and calculation cards to handle explain, describe, calculate and compare questions.
Potential difference across a component in terms of energy transfer
Potential difference (V) is the energy transferred per unit charge. It is the work done (W) in moving a unit charge (Q) between two points in a circuit. V = W / Q
What the Cambridge 9702 syllabus says
2025-2027 syllabus, in our words · AS LevelWhat the syllabus expects you to be able to do in this topic, in plain English. For the exact wording, see the official syllabus (PDF).
- Define a component's potential difference (p.d.) as the energy transferred for each unit of charge passing through it.
- Recall V = W / Q and use it.
- Recall and use the power equations P = VI, P = I²R and P = V² / R.
Cambridge syllabus keywords to use in your answers
These are the official Cambridge 9702 terms tagged to this section. Mark schemes credit responses that use the exact term — weave them into your answers verbatim rather than paraphrasing.
Tips to avoid common mistakes in Potential difference and power
- › Use the exact phrasing 'energy transferred per unit charge' to correctly represent the ratio of energy to charge.
- › Remember that potential difference is identical across all components connected in parallel; use P = V²/R to compare power dissipated.
- › Use R = V²/P to evaluate the resistance of components before predicting how current or power will change in new circuit configurations.
Define potential difference across a component in terms of energy transfer.
Potential difference (V) is the energy transferred per unit charge. It is the work done (W) in moving a unit charge (Q) between two points in a circuit. V = W / Q
A 12V battery transfers 600J of energy to a component. Calculate the charge that flows through the component.
Using V = W / Q, rearrange to find Q = W / V. Therefore, Q = 600J / 12V = 50 Coulombs.
What is the relationship between power, potential difference, and current?
Power (P) is the product of potential difference (V) and current (I). P = VI. This equation shows the rate at which electrical energy is converted into other forms of energy.
A resistor has a potential difference of 6V across it and a current of 0.5A flowing through it. Calculate the power dissipated by the resistor.
Using P = VI, power P = 6V * 0.5A = 3 Watts. This represents the rate at which electrical energy is converted into heat in the resistor.
State the equation that relates power, current, and resistance.
Power (P) equals the square of the current (I) multiplied by the resistance (R): P = I²R. This equation is useful when the current and resistance are known.
A 2Ω resistor has a current of 3A flowing through it. Calculate the power dissipated.
Using P = I²R, the power dissipated is P = (3A)² * 2Ω = 18 Watts.
State the equation that relates power, potential difference and resistance.
Power (P) equals the square of the potential difference (V) divided by the resistance (R): P = V²/R. This equation is useful when voltage and resistance are known.
A 10Ω resistor is connected to a 5V power supply. Calculate the power dissipated in the resistor.
Using P = V²/R, the power dissipated is P = (5V)² / 10Ω = 2.5 Watts.
Review the material
Read full revision notes on Potential difference and power — definitions, equations, common mistakes, and exam tips.
Read NotesMore topics in Unit 9 — Electricity
Potential difference and power sits alongside these A-Level Physics decks in the same syllabus unit. Each uses the same spaced-repetition system, so progress in one informs the next.
Key terms covered in this Potential difference and power deck
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