Trace electrical energy transfer through a circuit
Follow energy from a cell or mains source through components into their surroundings without treating charge as fuel.
Section P4.1 · Electrical quantities
Cross-referenced to the 2028–2029 0653 section using original teaching from the related single-science courses. A 0653-specific objective-by-objective and Core/Supplement review is in progress. Written practice is self-checked and does not demonstrate supervised laboratory competence or award an official Cambridge grade.
Before you begin
- Distinguish energy stores from pathways.
- Describe current as charge flow.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
Which describes the cell's starting store?
What you will learn
- Trace source, component and surroundings energy transfers.
- Separate useful outputs, other outputs and charge movement.
Choose the source and destination
A cell can supply energy from its chemical store through electrical transfers to circuit components. A lamp transfers energy to its surroundings by light and heating. A motor can transfer energy mechanically to a moving load, with additional heating and sound. Name the component and destination rather than ending the account at 'electrical energy'.
Mains supply provides an electrical transfer to an appliance; the original energy source depends on the electricity-generation system. Mains is not itself proof of one particular fuel or renewable resource. These descriptions are written accounts, not instructions to experiment with mains equipment.
Follow energy without consuming charge
In a complete circuit, charge carriers take part in the conducting path without being used up as fuel. The source and components exchange energy while the charge account remains separate. A lamp's warming does not show that electrons have disappeared or that current after the lamp must be smaller in the simple single-path model.
A useful output need not equal the total electrical input. If a device receives 100 J and produces 30 J of the intended output while its state returns unchanged, the other 70 J must be included in transfers to the surroundings. During warm-up, some energy can remain in the component's increased internal store, so do not automatically classify every unmeasured joule as already lost to the room.
Sources for this lesson
Pause and explain
A warming device receives 100 J and transfers 40 J out. What does the remaining 60 J represent under the stated boundary?
Worked example
A lamp receives 100 J, emits 30 J of useful light and has no net stored-energy increase over the interval. Find the other transfer.
Show the worked solution
- Electrical input is 100 J.
- Useful light is 30 J and storage change is zero.
- The remaining transfer is 100 − 30 = 70 J.
Answer 70 J transferred by other pathways to the surroundings.
Try a topic test
Choose Easy, Normal or Difficult. Save your answers and open worked review after finishing.
Test this topic →From guided practice to a new situation
Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
Trace energy from a cell through a lamp into its surroundings.
Give me a hint
Name the cell's store, electrical transfer and lamp outputs separately.
Compare my reasoning
- The cell's chemical store can decrease.
- Energy reaches the lamp electrically.
- The lamp transfers energy by light and heating.
Chemical store → electrical transfer → light and heating into the surroundings.
Look for these in your work
- Include source and destinations.
- Do not say charge is consumed.
A motor receives 200 J, transfers 120 J mechanically and has no net stored-energy increase. Find the other outward transfer.
Give me a hint
Use the stated unchanged-energy boundary before subtracting.
Compare my reasoning
- Input is 200 J.
- Mechanical output is 120 J.
- Other transfers total 200 − 120 = 80 J.
80 J by other outward pathways.
Look for these in your work
- State the interval boundary.
- Balance the full input.
An appliance receives 100 J while warming and transfers 40 J to its surroundings. Can all the other energy already have reached the room?
Give me a hint
Retain an internal-store change in the device's energy balance.
Compare my reasoning
- Input is 100 J and outward transfer is 40 J.
- The difference is 60 J retained in the device over the interval.
- Its warming is consistent with an increased internal store.
No; 60 J remains as an increased store under the supplied account.
Look for these in your work
- Include storage.
- Do not destroy or double-count energy.
Common mistakes
- Charge is not used up as energy fuel.
- Mains does not identify the original generation resource.
- Include storage changes during warm-up.
What can you explain now?
Where can energy go after entering a lamp electrically?
Compare with the explanation
Into the surroundings by light and heating.
Trace both the useful output and other transfers while retaining a separate charge account.
After trying it yourself, choose your next review. This is your self-assessment.
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Make it stick
Trace a source–component–surroundings energy account while separating charge flow and stored-energy changes.
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.