Page 33 - Teach Yourself Electricity and Electronics

Resistors 13

1-5 In a conductor, electrons are passed from atom to atom.

Electrical insulators can be forced to carry current. Ionization can take place; when
electrons are stripped away from their atoms, they have no choice but to move along.
Sometimes an insulating material gets charred, or melts down, or gets perforated by a
spark. Then its insulating properties are lost, and some electrons flow.
An insulating material is sometimes called a dielectric. This term arises from the
fact that it keeps electrical charges apart, preventing the flow of electrons that would
equalize a charge difference between two places. Excellent insulating materials can be
used to advantage in certain electrical components such as capacitors, where it is im-
portant that electrons not flow.
Porcelain or glass can be used in electrical systems to keep short circuits from oc-
curring. These devices, called insulators, come in various shapes and sizes for different
applications. You can see them on high-voltage utility poles and towers. They hold the
wire up without running the risk of a short circuit with the tower or a slow discharge
through a wet wooden pole.

Resistors

Some substances, such as carbon, conduct electricity fairly well but not really well. The
conductivity can be changed by adding impurities like clay to a carbon paste, or by wind-
ing a thin wire into a coil. Electrical components made in this way are called resistors. They
are important in electronic circuits because they allow for the control of current flow.
Resistors can be manufactured to have exact characteristics. Imagine telling each
person in the line that they must pass a certain number of balls per minute. This is anal-
ogous to creating a resistor with a certain value of electrical resistance.
The better a resistor conducts, the lower its resistance; the worse it conducts, the
higher the resistance.