Energy transferred = charge × potential difference (E = QV)
Energy transferred = charge flow × potential difference, or E = Q V. E is the energy in joules (J), Q is the charge in coulombs (C) and V is the potential difference in volts (V). Every GCSE physics specification puts it on the recall list, and since 2025 your exam paper prints it on the equation sheet as well.
Equation
E = Q V
| Symbol | Quantity | Unit |
|---|---|---|
E | energy transferred | J |
Q | charge | C |
V | potential difference | V |
What each specification says
| Exam board | Status | Equation |
|---|---|---|
| AQA Physics (8463) | Recall | E = Q V |
| AQA Combined Science (8464) | Recall | E = Q V |
| Edexcel Physics (1PH0) | Recall | E = Q V |
| Edexcel Combined Science (1SC0) | Recall | E = Q V |
| OCR Gateway Physics A (J249) | Recall | E = Q V |
| OCR Twenty First Century Physics B (J259) | Recall | E = Q V |
Calculator: E = Q V
Equation
V = E ÷ Q
| Symbol | Quantity | Unit |
|---|---|---|
V | potential difference | V |
E | energy transferred | J |
Q | charge | C |
What each specification says
| Exam board | Status | Equation |
|---|---|---|
| AQA Physics (8463) | Not in this specification | |
| AQA Combined Science (8464) | Not in this specification | |
| Edexcel Physics (1PH0) | Not in this specification | |
| Edexcel Combined Science (1SC0) | Not in this specification | |
| OCR Gateway Physics A (J249) | Not in this specification | |
| OCR Twenty First Century Physics B (J259) | Recall | V = W/Q |
Calculator: V = E ÷ Q
What the equation tells you
Charge is the stuff that flows round a circuit, carried by electrons in a metal wire. We measure it in coulombs. Potential difference, often called voltage, tells you how much energy each coulomb gains or loses between two points.
So one volt means one joule for every coulomb. A 9 V battery gives each coulomb 9 J as it passes through. If 100 C flow through that battery, it hands over 900 J to the circuit. The energy then goes into the bulb, motor or heater that the charge flows through.
You often need the charge first. The charge equation Q = I t gets it from the current and the time. After that, E = Q V finishes the job.
The printed forms on each board
AQA, Edexcel and both OCR courses print this equation as E = Q V, in Physics and in Combined Science. The word form differs a little: AQA says charge flow, while Edexcel says charge moved.
OCR Twenty First Century Physics (J259) goes one step further. Its recall list also has potential difference = work done ÷ charge, printed as V = W/Q. That is the same idea with V as the subject. The OCR Twenty First Century page lists all 32 of its equations.
Recall is the specification's own label for this group. In the exam hall it makes no difference, because the sheet in every paper from 2025 prints the whole list. The full comparison is on our physics equation sheet guide.
Rearranged forms
- Q = E ÷ V, to find the charge
- V = E ÷ Q, to find the potential difference
A quick check helps here. Energy is always the biggest number when the voltage is above 1 V, because it is the charge multiplied up. If your energy comes out smaller than your charge in a mains circuit, you divided by mistake.
This equation sits beside V = I R in most circuit questions, so check which one the numbers fit.
Worked examples
E
- E = Q V
- E = 1800 × 5
- E = 9000 J
9000 J
Q
- Turn kilojoules into joules: 46 kJ = 46 000 J
- Q = E ÷ V
- Q = 46 000 ÷ 230
- Q = 200 C
200 C
V
- V = E ÷ Q
- V = 3 ÷ 0.5
- V = 6 V
6 V
Common mistakes
- Using the current in place of the charge. Current is charge per second, so you must multiply by the time before E = Q V will work.
- Mixing up the two Vs. In this equation V is potential difference in volts, and the unit V is also volts, so write the unit after every number to keep them apart.
- Keeping energy in kJ while the answer asks for coulombs. 46 kJ divided by 230 V gives 0.2, which is 1000 times too small.
Try turning E = Q V into Q = E ÷ V at speed in the Equation Rearranger.
Questions people ask
What is one volt in plain words?
One volt means that each coulomb of charge carries one joule of energy between two points in a circuit.
How is E = QV different from E = Pt?
Both give energy in joules. E = Q V uses charge and voltage, while E = P t uses power and time. Pick the one that matches the values in the question.