Brainlag PlusHow rubbing two insulators charges them, why charged objects attract or repel, and where sparks come from.
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 9 practice questions are in Plus.
Screen 1 of 4, free to read.
- 9 exam-style questions, marked as you go, each with a worked solution
- Anything you get wrong is saved to your flashcards