Calculating Energy Transfers
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Calculating energy transfers
Charge flowing through a component is the battery doing work on it, and the energy handed over depends on three things: how hard the charge is pushed (voltage), how much flow there is (current) and how long the flow lasts (time). Multiply the three and you have the energy transferred in joules.
What you know already
When charge is driven around a circuit, the battery is doing work — and work done is energy transferred. This note assembles the three quantities that set the size of that transfer, the current, the voltage and the time in seconds, into the single equation E = I × V × t, and shows it is just power multiplied by time.
Key points of understanding
- Work done by the moving charge equals the energy transferred in the circuit.
- Energy transferred depends on the current, the voltage and the time the component runs.
- The equation of record is E = I × V × t, with energy in joules.
- It is E = P × t with the power written as P = I × V.
- Time must enter the equation in seconds, never minutes.
- The energy the battery supplies equals the total transferred to every component.
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1.Calculating energy transfers
Charge flowing through a component is the battery doing work on it, and the energy handed over depends on three things: how hard the charge is pushed (voltage), how much flow there is (current) and how long the flow lasts (time). Multiply the three and you have the energy transferred in joules.
Key points
- Work done by the moving charge equals the energy transferred in the circuit.
- Energy transferred depends on the current, the voltage and the time the component runs.
- The equation of record is E = I × V × t, with energy in joules.
- It is E = P × t with the power written as P = I × V.
- Time must enter the equation in seconds, never minutes.
- The energy the battery supplies equals the total transferred to every component.
First pass
Energy transferred equals current × voltage × time; the longer a device runs, the more energy it moves.
Analogy — Filling a paddling pool: the flow rate (current), the pressure (voltage) and the filling time together set the water collected.
Exam pointer — Convert minutes to seconds before substituting — this single slip loses the most marks here.
Going deeper
Because P = I × V, the same law can be read as E = P × t; the two forms are one relationship seen two ways.
Analogy — A taxi fare: the rate per mile (power) times the miles driven (time at speed) gives the total paid (energy).
Exam pointer — 'Work done' and 'energy transferred' are interchangeable in mark schemes — use either name confidently.
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