Section 1 of 4Conductors
Metals
- Silver, copper, aluminium and steel are good conductors because they allow charge to flow through them easily.
Delocalised electrons
- The outer electrons of metal atoms are not tied to one atom, so they are free to move through the metal.
Current
- An electric current is the rate of flow of these charges, so free electrons make metals excellent conductors.
Uses
- Copper is used for wires and cables because it carries current with little loss of energy.
Section 2 of 4Insulators
Insulators
Examples
- Rubber, plastic, glass and dry wood do not let charge move through them easily.
Why
- Their electrons are held firmly in place, so there are no free charges to carry a current.
Uses
- Plastic covers on cables and rubber mats protect people from electric shock.
Static charge
- Charge placed on an insulator stays where it is, which makes insulators able to hold static charge.
| Property | Conductor | Insulator |
|---|---|---|
| Free charges | Yes, delocalised electrons | No |
| Allows current | Easily | Hardly at all |
| Holds static charge | Only if insulated from earth | Yes |
| Examples | Copper, silver, steel | Rubber, glass, polythene |
Section 3 of 4Charge and Earthing
1
When two insulators are rubbed together, electrons move from one surface to the other, leaving one positive and one negative.
2
The charge cannot spread out or escape, because an insulator does not let electrons move through it.
3
If a charged conductor is touched or connected to earth, electrons flow and the charge is conducted away.
4
A metal object held in the hand cannot be charged by rubbing, because the charge leaks away through the body to the ground.
5
A metal rod fitted with an insulating handle can be charged, because the handle stops the charge escaping.
Section 4 of 4Exam Checklist & Tips
2.4.1 – Key Points for the Exam
- Conductor A material that allows electric charge to flow through it easily.
- Insulator A material that does not allow electric charge to flow through it easily.
- Delocalised electron An electron that is free to move through the structure rather than belonging to one atom.
- Static electricity Electric charge that builds up on the surface of an insulator and stays there.
- Earthing Providing a conducting path to the ground so that charge can drain away.
Common Mistakes
- Saying electrons move through insulators with difficulty; there are essentially no free charges.
- Stating that conductors cannot be charged at all; they can if they are insulated from earth.
- Thinking that current is made of positive charges moving in a metal; it is the movement of electrons.
- Describing the charge on an insulator as flowing away; it stays put until a conductor touches it.