Potential difference measures how much energy each coulomb of charge gives up as it passes through a component. Multiply by the current and you have the rate of energy transfer: the power.
The potential difference across a component is the energy transferred per unit charge, V = W / Q, measured in volts (one joule per coulomb). The electrical power, the rate of energy transfer, is P = VI, which combines with V = IR to give the equivalent forms P = I²R and P = V² / R.
Set the voltage across a resistor and the current follows from V = IR; watch the power dissipated track P = VI and the three equivalent forms agree at every setting.
Pick the form that matches the quantities you are given.
| Relation | Use | Unit |
|---|---|---|
| V = W / Q | potential difference | volt (V) |
| P = VI | power from voltage and current | watt (W) |
| P = I²R | when current and resistance are known | watt (W) |
| P = V² / R | when voltage and resistance are known | watt (W) |
Four quick checks tied to this lesson. Each correct answer earns XP and lights this skill on your star map.
The potential difference across a component is the:
The volt is equivalent to:
A component has 12 V across it and carries 2.0 A. The power dissipated is:
A 5.0 A current flows through a 4.0 Ω resistor. The power dissipated is:
All three power formulas are equivalent through V = IR.
The three power formulas are equivalent, not different physics: pick the one matching your known quantities. Watch the squares: in P = I²R doubling the current quadruples the power, and in P = V²/R doubling the voltage quadruples it. Potential difference is energy per charge (J C⁻¹), not energy per second.
Unlocks once the checks above are done. Worth more XP, written to AS Paper 1 and 2 standard.
A charge of 8.0 C transfers 96 J of energy through a lamp. The potential difference across the lamp is:
A 230 V heater has a resistance of 23 Ω. Its power is:
If the current through a fixed resistor is doubled, the power dissipated becomes:
This skill is now lit gold on your star map. Keep the chain going.