The materials used in electronics can be divided into three basic types.

To understand why the properties of these differ you need, at least, to know the smallest possible amount about...

Moving charges

and Quantum Mechanics


Conductors

Most of the conductors used in electronics are metals like copper, aluminium and steel. Conductors are materials that obey Ohm's law and have very low resistance. They can therefore carry electric currents from place to place without dissipating a lot of power. As a result, metals are useful as connecting wires to carry electrical signals from place to place. They help ensure that most of the signal's power reaches it's destination instead of warming up the wires in between!

In fact, although it sounds odd, modern resistors are also made of conductor materials. However, they use very thin pieces of conductor which don't pass current too easily.


Insulators

Glass, most polymers (plastics), rubber and wood are all examples of insulators. These are materials which will refuse to carry an electric current. They are useful for jobs like coating electric wires to prevent them from 'shorting together' or giving you a shock. Silk and cotton are also good insulators (when they're dry!!) and some of the mains wiring in very old houses once used them - but by modern standards this was pretty dangerous since you could get a shock when wet or a spark would set them alight when dry!

Modern insulators like PVC (PolyVinylChloride) are much better and safer.

Insulators are also very useful to fill the 'gap' in between the metal plates of a capacitor. Very old capacitors (and some modern radio ones) use air gaps since air is a good insulator.


Semiconductors

All the transistors, diodes, integrated circuits, etc. used in modern electronics are built using a range of semiconductors. The basic property of a semiconductor is given away by its name - it 'conducts a little bit'. A semiconductor will carry electric current, but not as easily as a normal conductor.

Some materials are intrinsic semiconductors. The semiconducting properties occur in these materials naturally. However, most of the semiconducting materials used in electronics are extrinsic. This means that left to themselves they are excellent insulators. These materials are turned into semiconductors by doping them with small amounts of foreign atoms. The number of doping atoms you need to add is very small. If you left all the doping atoms inside the package of a transistor and removed the bulk of the material you'd be left with a vacuum better than exists between the planets of the solar system!


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