Explain conduction and insulation using a simple electron model
Explain why mobile electrons allow metals to carry charge while ordinary insulating materials restrict charge movement.
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 electrons as negatively charged.
- Describe a complete low-voltage sample test.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
What separates neutral from particle-free?
What you will learn
- Explain metallic conduction with mobile electrons.
- Contrast ordinary insulators and distinguish net neutrality from carrier mobility.
Mobile electrons in a metal
In the simple metal model, some electrons are free to move through the solid among positive ions. An electrical driving influence can give their otherwise random motion a directed movement, allowing charge to be transferred through a connected path. The positive ions stay at lattice sites apart from local vibration; they do not travel along the wire to explain ordinary metallic conduction.
A metal can be neutral overall and still conduct. Net neutrality balances its total positive and negative charge, while conduction depends on whether carriers can move. Charging a conductor and connecting it to another conductor can let electrons redistribute or transfer; these are distinct from creating charge.
Bound charge in an ordinary insulator
In ordinary dry plastic, glass or rubber, electrons are much more strongly bound and cannot move freely through the bulk as in a metal under the school test conditions. A rubbed insulating rod can therefore retain a local charge more readily than an object with a conducting connection to Earth.
Insulators still contain charged particles and their bound charge can polarise slightly. Insulation does not mean particle-free or incapable of every electrical response. Moisture and sufficiently different conditions can change the observed behaviour. This introductory electron model explains ordinary solid examples; it is not a claim that every conducting medium uses mobile electrons alone.
Sources for this lesson
Pause and explain
Why does dry plastic behave as an insulator in the simple test?
Worked example
A neutral copper wire carries charge through a connected circuit. Explain why neutrality does not prevent conduction.
Show the worked solution
- The total positive and negative contributions balance.
- Some electrons remain mobile within the metal.
- A driving influence can produce directed charge movement through the path.
Answer Neutral copper can conduct because it contains mobile electrons despite zero net charge.
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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 electrical conduction in a copper sample using the simple electron model.
Give me a hint
Identify the mobile constituent and the fixed positive structure.
Compare my reasoning
- Copper has mobile electrons among positive ions.
- The driving influence produces directed electron movement.
- Charge can pass through a complete conducting path.
Mobile electrons carry charge through copper; positive ions remain at lattice sites.
Look for these in your work
- Name the carriers.
- Keep the positive solid structure in place.
Compare a neutral metal and a neutral dry plastic sample without saying one has no electrons.
Give me a hint
Both can have balanced net charge; compare carrier mobility.
Compare my reasoning
- Both contain balanced positive and negative contributions.
- The metal has electrons mobile through the bulk.
- The plastic's electrons are strongly bound in this model.
Both are neutral; the metal has mobile electrons, while ordinary dry plastic restricts their bulk movement.
Look for these in your work
- Separate balance from mobility.
- Explain the insulation mechanism.
A rubbed insulating rod is held by a dry insulating handle; a metal sample is connected to Earth. Explain their different charge-retention conditions.
Give me a hint
Compare available charge-transfer paths, not the absence of charged particles.
Compare my reasoning
- The dry insulating handle restricts electron transfer away.
- The metal's mobile electrons and Earth connection allow transfer.
- The connected metal need not retain the same local charge.
The insulating support limits leakage; the connected metal provides a transfer path to or from Earth.
Look for these in your work
- Include the stated connection.
- Do not assume every isolated conductor instantly loses all charge.
Common mistakes
- Neutral does not mean no mobile electrons.
- Positive metal ions do not travel along the wire.
- Insulators contain charged particles with restricted bulk movement.
What can you explain now?
Which carriers move through a metal in the simple model?
Compare with the explanation
Free electrons.
Positive ions retain their lattice sites while mobile negative electrons carry the charge.
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Make it stick
Explain carrier mobility, ordinary insulation and charge retention without confusing these with net neutrality.
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.