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Static electricity and electric fields
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Rubbing insulators together can build up charge. Static can be useful and dangerous. Separate Physics only.
Charging by friction
When two insulators are rubbed together, electrons are transferred from one to the other.
The material that gains electrons becomes negative; the one that loses electrons becomes positive.
Only electrons move: positive charges do not.
The material that gains electrons becomes negative; the one that loses electrons becomes positive.
Only electrons move: positive charges do not.
Forces and fields
Like charges repel; unlike charges attract.
A charged object has an electric field around it. Field lines point away from positive charges and towards negative charges.
The field is stronger closer to the charge.
A charged object has an electric field around it. Field lines point away from positive charges and towards negative charges.
The field is stronger closer to the charge.
Uses and dangers
Uses: paint spraying, photocopiers and printers, dust removal in chimneys.
Dangers: sparks when refuelling aircraft or cars could ignite fuel vapour. Earthing lets the charge flow safely away.
Lightning is a large discharge of static.
Dangers: sparks when refuelling aircraft or cars could ignite fuel vapour. Earthing lets the charge flow safely away.
Lightning is a large discharge of static.
A polythene rod becomes negative when rubbed with a cloth. Explain why.
- Electrons move from the cloth to the rod.
- The rod gains electrons, so it has a negative charge.
Answer: The rod gains electrons from the cloth.
Rubbing transfers electrons. Gaining electrons makes an object negative. Like charges repel, unlike attract. Earthing removes charge safely.
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