AQA · GCSE · Physics
Course version: 8463 · Version from Sept 2016
When certain insulating materials are rubbed against each other they…
Full specification wording
Static charge: When certain insulating materials are rubbed against each other they become electrically charged.
Rubbing two insulators together drags electrons from the surface of one onto the surface of the other.
Checked against the AQA 8463 specification (opens in a new tab) on .
- Point 1 of 9
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Rubbing two insulators together drags electrons from the surface of one onto the surface of the other. Which way they go depends on the pair of materials, not on how hard you rub: rubbing a polythene rod with a cloth leaves the rod negative and the cloth positive, while rubbing an acetate rod with the same cloth leaves the rod positive. The materials must be insulators for the effect to show, because charge cannot move through an insulator and so stays where the rubbing put it. Do the same with a metal rod held in your hand and the charge flows away to earth through you, leaving the rod apparently uncharged. Only electrons move, because the positive nuclei are fixed, so a positively charged object is one that has lost electrons.
What earns the marks
- Electrons being transferred from one material to the other by rubbing.
- The material gaining electrons becoming negatively charged.
- The material losing electrons being left positively charged.
- The materials needing to be insulators so that the charge cannot flow away.
Common mistakes and how to put them right
Saying protons or positive charges are transferred by rubbing, which is not credited at all.
Writing 'positive electrons', which loses the mark even when the rest is right.
Claiming charge is created by friction rather than transferred between the materials.
Expecting a metal rod held in the hand to stay charged after rubbing.
Exam tips
- Every static answer should name electrons and say which way they moved.
- Only ever move negative charge in your explanation, because nothing positive travels.
- If two materials are named, state which becomes positive and which becomes negative.
Try the lesson
The start of the Static charge: When certain insulating materials are rubbed against each other they become electrically charged. lesson, made from checked teaching notes for this specification point.
Have a go first
What happens to the electrical charge on two insulating materials when they are rubbed together?
Listen
Rubbing two insulators together drags electrons from the surface of one onto the surface of the other. Which way they go depends on the pair of materials, not on how hard you rub: rubbing a polythene rod with a cloth leaves the rod negative and the cloth positive, while rubbing an acetate rod with the same cloth leaves the rod positive. The materials must be insulators for the effect to show, because charge cannot move through an insulator and so stays where the rubbing put it. Do the same with a metal rod held in your hand and the charge flows away to earth through you, leaving the rod apparently uncharged. Only electrons move, because the positive nuclei are fixed, so a positively charged object is one that has lost electrons. A strong answer earns marks for these points. electrons being transferred from one material to the other by rubbing. the material gaining electrons becoming negatively charged. the material losing electrons being left positively charged. the materials needing to be insulators so that the charge cannot flow away. Exam tip: Every static answer should name electrons and say which way they moved.
See it
Key words
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charging by friction
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electron transfer
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insulators
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positive by loss of electrons
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See every definition
- charging by friction
- Rubbing certain insulating materials against each other makes them electrically charged, as electrons are dragged from the surface of one onto the surface of the other.
- electron transfer
- Only electrons move when materials are rubbed together, because the positive nuclei are fixed, so charge is transferred between the materials rather than created.
- insulators
- The materials must be insulators for the effect to show, because charge cannot move through an insulator and so stays where the rubbing put it.
- positive by loss of electrons
- A positively charged object is one that has lost electrons, since only electrons move and the positive nuclei are fixed.
Label the diagram
Some boxes have lost their names. Pick the right name for each number.
1Box 1
2Box 2
3Box 3
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