Explain why a static charge builds up when two insulating materials are rubbed together, and why the same effect does not occur when two conducting materials are rubbed together.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
Rubbing transfers electrons from one insulating object to the other.
The insulator that gains electrons becomes negatively charged, while the one that loses electrons becomes positively charged.
In insulators the electrons are fixed and cannot move through the material, so the charge remains on the surface as static charge.
In conductors the electrons are free to move, so any charge that builds up quickly flows away, keeping the conductors neutral.
The insulator that gains electrons becomes negatively charged, while the one that loses electrons becomes positively charged.
In insulators the electrons are fixed and cannot move through the material, so the charge remains on the surface as static charge.
In conductors the electrons are free to move, so any charge that builds up quickly flows away, keeping the conductors neutral.
Examiner tips
- Use the word ‘transfer’ to show understanding of electron movement. Show the two charges (negative/positive) and explain why they stay on insulators. Mention that conductors allow electron flow to cancel the charge.
- Include the key terms: ‘insulator’, ‘conductor’, ‘static charge’, ‘free electrons’.
Common mistakes
- Saying the charge builds up on conductors instead of insulators. Forgetting to explain why the charge does not remain on conductors. Using vague terms like ‘electricity’ instead of ‘electrons’ and ‘static charge’.
Mark scheme (4 marks)
- Rubbing transfers electrons from one insulating object to the other
- One insulator gains electrons giving it a negative static charge, and the other loses electrons giving it a positive static charge
- In insulators, electrons are fixed and cannot flow through the material, so the charge cannot be cancelled out and remains as static charge
- In conductors, electrons are free to move (delocalised), so any charge that builds up quickly flows away, keeping the conductors neutral
Key terms in this question
Related
- All Edexcel GCSE Physics (1PH0) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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