How rubbing two insulators charges them, why charged objects attract or repel, and where sparks come from.
What you will learn
- Explain charging by friction in terms of electrons
- Predict attraction and repulsion between charged objects
- Explain why a charged object attracts an uncharged one
- Explain sparks, shocks and earthing
Charging by rubbing
When two insulating materials are rubbed together, friction moves electrons from one to the other.
Only electrons move: the protons stay fixed in the nuclei.
- The material that gains electrons becomes negatively charged.
- The material that loses electrons becomes positively charged.
- The two charges are equal in size and opposite in sign: no charge is made or destroyed.
- A polythene rod rubbed with a woollen cloth becomes negative
- Electrons have moved from the cloth onto the rod
- The cloth is left with an equal positive charge
Charge stays put on an insulator. On a metal it would flow away through your hand, which is why charging by rubbing is done with insulators.
The rest of this lesson and its 10 practice questions are locked.
In this lesson
- Charging by rubbing
- Attract or repel
- Sparks and earthing
- Try it: Which way did the electrons go?
10 practice questions, marked as you go; about 20 minutes in all.
Key terms
Electrons, Gains, Negatively, Loses, Positively, Non-contact, Repel, Attract, Spark, Electrostatic sprayer
In this unit: Mains electricity, the National Grid and static
Direct and alternating current, the three-core cable and plug, electrical power and energy, the cost of electricity, the National Grid and transformers, and static charge and electric fields.