Relate electric current to charge flow
Describe current through a chosen point and distinguish moving charge from energy transferred by the circuit.
Section P4.2.2 · Current
Cross-referenced from the related Cambridge IGCSE Chemistry 0620 or Physics 0625 teaching to the 0652 syllabus. Exact 0652 Core/Supplement objective coverage and this final-series course’s examiner fit still need specialist review. Written practice is self-checked and does not predict a Cambridge grade or demonstrate supervised laboratory competence.
Before you begin
- Identify electric charge signs.
- Recognise a complete conducting path.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
Which constituent is mobile in the simple metal model?
What you will learn
- Relate current to the flow of electric charge.
- Distinguish a moving charge account from an energy account.
Choose where charge passes
Electric current is related to the flow of charge. Imagine a marked cross-section of a wire: charge carriers pass through that section. A charge sitting on an insulated rod can exert an electrostatic force without a sustained current through a connected wire; a net charge value by itself does not specify flow.
A closed path containing a suitable source can maintain current through its components. Opening the single path stops sustained conduction in the simple circuit model. The carriers are already present in the materials, so a lamp need not wait for one particular electron to complete a whole journey from the cell.
Keep charge and energy separate
The source transfers energy electrically through the circuit and components transfer energy into other stores or pathways. Charge is not used up as a fuel in the lamp. A current observation concerns the movement of charge, while a heating or lighting observation concerns energy transfer.
Use the stated carrier model for the material. Metals conduct through mobile electrons; other conducting media can have different mobile carriers. This lesson introduces the flow idea qualitatively. The numerical charge-per-time equation and conventional-current direction are introduced separately in the Extended lessons.
Sources for this lesson
Pause and explain
What does a current through a marked wire section describe?
Worked example
A learner says a lamp uses up electrons, so only empty wire remains after it. Explain the error.
Show the worked solution
- The wire already contains charge carriers.
- The circuit transfers energy through the lamp.
- Charge is not consumed as a fuel by the lamp.
Answer The lamp transfers energy; charge carriers are not used up.
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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.
Describe what current means at a marked cross-section of a conducting wire.
Give me a hint
Name the flowing quantity and the location where its passage is considered.
Compare my reasoning
- Select the wire cross-section.
- Charge carriers move through it.
- That charge flow is related to the electric current.
Current concerns electric charge flowing through the chosen cross-section.
Look for these in your work
- Name charge flow.
- Keep the reference location explicit.
A charged insulating rod sits still on a dry support. Does its net charge alone prove sustained current through a wire?
Give me a hint
Compare a charge balance with a connected flow path.
Compare my reasoning
- The rod has a static net charge.
- No sustained wire path or carrier passage is specified.
- The charge value alone does not establish a current.
No; a static charge value does not alone show sustained charge flow.
Look for these in your work
- Distinguish charge from flow.
- Identify the missing path information.
Explain why light from a lamp does not mean the charge carriers are used up.
Give me a hint
Trace the energy transfer separately from the carrier account.
Compare my reasoning
- The source supplies an electrical energy transfer.
- The lamp transfers energy by light and heating.
- Charge carriers continue to take part in the conducting path.
Energy is transferred in the lamp; charge is not consumed as a fuel.
Look for these in your work
- Name the energy outcome.
- Retain charge carriers in the circuit account.
Common mistakes
- Charge and energy are different accounts.
- Static charge does not alone establish sustained flow.
- Use a complete path for the simple sustained-current model.
What can you explain now?
What flows when there is an electric current?
Compare with the explanation
Electric charge.
Current describes charge movement through a chosen point or section of the conducting path.
After trying it yourself, choose your next review. This is your self-assessment.
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Make it stick
Explain current as charge flow through a chosen point and distinguish it from stored charge and energy transfer.
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.