Knowledge Organiser: Potential Difference
Key Terms
- Potential difference: Energy per unit charge (V)
- Volt: 1 J per coulomb
- P.d. across a supply: Energy given by supply per coulomb
- Voltmeter: Measures p.d.; in parallel
Key Facts
- Series: voltages add up to supply
- Parallel: same voltage across each branch
- Voltmeter in parallel; ammeter in series
- 1 V = 1 J/C
Key Equations
- V = E / Q
- E = V × Q
- Q = E / V
Exam Tips
- Voltmeter = parallel (always)
- Series: missing V = supply − others
- Parallel: all branches = supply voltage
- State units: V, J, C
Common Mistakes
- Placing voltmeter in series: Voltmeters must always be connected in parallel across a component — never in series
- Confusing voltage and energy: Voltage (V) is energy per unit charge (J/C) — it is not the same as energy; a large voltage does not mean a large total energy
- Forgetting voltage splits in series: In a series circuit, voltages across components add up to the supply voltage — always check they sum correctly
- Saying voltage is "used up": Voltage is a measure of energy transferred per coulomb — the charge carries less energy after passing through a component, but charge itself is conserved
Memory Aid
- For V = E/Q — the Ski Lift:
- The Voltage is the Elevation (energy) given to each Quantity of charge (coulomb). The battery is the ski lift that raises each coulomb to a higher "energy height."
- Voltmeter vs Ammeter connection — "V is a visitor, A is in the action":
- The Voltmeter is a Visitor — it stands alongside (parallel), watching what happens across a component. The Ammeter is in the Action — it stands in the flow itself (series), part of the circuit.
- Series vs Parallel voltage rule — "Series Shares, Parallel Pairs":
- In a series circuit, the voltage is shared (split) between components. In a parallel circuit, every branch gets the same voltage as the supply.