Explain metallic current as moving free electrons
Describe directed electron movement through a metal without moving its positive lattice ions or consuming its carriers.
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
- Recall the simple metallic electron model.
- Relate current to charge flow.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
What does neutral mean for a whole object?
What you will learn
- Explain metallic electrical conduction with free electrons.
- Separate microscopic motion, directed flow and the lattice structure.
Use the carriers already present
A metal contains mobile free electrons among positive ions. The ions remain at their lattice sites apart from local vibration. Under an electrical driving influence, electron motion has a directed component through the metal, and the moving negative charge accounts for metallic current.
The electrons also have microscopic motion that is not a simple identical straight march. The directed drift is an average component of that motion. A wire can remain nearly neutral overall while charge moves through it, so net neutrality does not prevent current.
Keep the microscopic and circuit accounts consistent
A source maintains the electrical driving influence around a complete path; the carriers are not created at the cell and then destroyed at the lamp. When a switch closes, a circuit response can occur much sooner than a particular electron's full journey around the wire. Do not confuse slow average carrier drift with the speed at which the circuit establishes its electrical response.
This explanation is for ordinary metallic conductors. Other conducting materials may use ions or other carriers, so 'all current is electrons' is too broad. The opposite conventional-current direction used for circuit arrows is introduced in its own Supplement lesson.
Sources for this lesson
Pause and explain
Which statement describes a metal carrying current?
Worked example
A neutral metal wire carries current. Name the moving carriers and explain why neutrality is compatible with flow.
Show the worked solution
- Some electrons are mobile in the metal.
- Positive ions remain at lattice sites.
- The total charge can balance while electrons have directed movement.
Answer Mobile electrons carry charge; a balanced net charge does not prevent their directed movement.
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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.
Explain conduction in a metal carrying current.
Give me a hint
Identify the mobile and lattice constituents separately.
Compare my reasoning
- Free electrons are mobile.
- An electrical driving influence produces directed movement.
- Positive ions remain at lattice sites apart from vibration.
Directed free-electron movement carries charge through the metal.
Look for these in your work
- Name electrons.
- Retain the positive lattice structure.
A metal has zero net charge but a non-zero current. Explain why this is possible.
Give me a hint
Compare a balance of charge with motion through a marked section.
Compare my reasoning
- Net zero describes balanced total contributions.
- Mobile electrons can still pass through a section.
- Charge flow can therefore occur in a nearly neutral wire.
Balanced net charge and mobile-electron flow describe different properties.
Look for these in your work
- Explain both accounts.
- Avoid treating neutral as particle-free.
A learner says the lamp must wait for an electron to drift all the way from the cell after the switch closes. Assess the claim.
Give me a hint
Remember the carriers throughout the path and the establishment of the circuit response.
Compare my reasoning
- Carriers already exist in the entire wire.
- The electrical influence establishes a response along the path.
- One electron's complete journey is not the required waiting time.
No; carriers already present respond before a particular electron completes a whole circuit journey.
Look for these in your work
- Distinguish response from drift.
- Do not assign an unprovided numerical speed.
Common mistakes
- Positive lattice ions do not travel along the wire.
- Net neutrality does not imply no current.
- Carrier drift and circuit-response speed are different.
What can you explain now?
Which carriers explain ordinary metallic current?
Compare with the explanation
Free electrons.
Their directed movement carries negative charge through the metal while the lattice ions stay in place.
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Make it stick
Explain metallic current with directed mobile-electron motion and a retained lattice structure.
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.