Conductors and insulators
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The idea
Inside, a cable is made of copper; outside, of plastic. Why not all copper or all plastic? Because some materials let current through and others do not.
What to remember
- Conductor
A conductor lets electric current through well. All metals are conductors, for example copper, iron and aluminium.
- Insulator
An insulator (also called a non-conductor) hardly lets any electric current through, for example plastic, rubber, glass, wood and porcelain.
| Material | Conductor or insulator? |
|---|---|
| Copper | Conductor |
| Iron | Conductor |
| Aluminium | Conductor |
| Graphite (pencil lead) | Conductor |
| Plastic | Insulator |
| Rubber | Insulator |
| Glass | Insulator |
| Wood (dry) | Insulator |
Water can conduct, too
Tap water and salt water conduct electricity because substances are dissolved in them. That is why wet hands and electricity are a dangerous mix. More on the page “Staying safe”.
Example
Why a cable has two parts
The copper wire inside is a conductor: the current flows in it. The sheath of plastic is an insulator: it protects you when you touch the cable and stops two wires from touching each other.
Practice
Exercise
Solution
Copper right answer
Copper is a metal and conducts electricity very well. That is why cables are made of copper inside.
Iron right answer
Iron is a metal too and conducts electricity.
Rubber
Rubber does not conduct electricity. That is why it is suitable as a sheath around cables and on handles.
Glass
Glass does not conduct electricity and is an insulator.
All metals are conductors. Rubber and glass are insulators.
More on it:
Exercise
Solution
Plastic, an insulator right answer
Plastic does not let current through. That is why you can touch the sheath safely.
Copper, a conductor
Copper is the wire inside. It conducts the current and would be dangerous as a sheath.
Iron, a conductor
Iron conducts electricity and is not suitable as a protective sheath.
The sheath must be an insulator so that the current flows only in the wire and you are protected.
More on it:
Exercise
Solution
Right answer: The statement is true.
Salts are dissolved in tap water, and they let current through. Pure, distilled water hardly conducts.
More on it: