There are two main methods that are used to make resistors.
• The most common is to just have a bunch of wire wound up inside that little cylinder.
• Known as wire-wound resistors, they depend on the fact that a certain length of a
certain piece of wire will have a certain resistance.
• These resistors tend to be very reliable (with low tolerances), but cost more because of
the price of metals used in them and the machinery needed to carefully cut and wind the
wire.
• The other type of resistor is made of a piece of
carbon.
• Known as a composition resistor, they
depend on the size of the piece of carbon,
and the fact that carbon is a metalloid (has
some metal-like properties) that does
conduct electricity.
• Because they are made from cheap
carbon, composition resistors can cost
much less than similar wire-wound
resistors. The drawback is that the carbon
can be cracked while making them, or become cracked in use. They have higher
tolerances because of the uncertainty in cutting the carbon.
In some cases it is necessary to have a circuit with resistors that you can adjust.
• These resistors are known as potentiometers or variable resistors.
• Often they are just a modified version of a wire-wound resistor, although newer
versions use advanced electronics instead.
• You’ve used one if you’ve ever used a dimmer switch for lights in a room, or played with an
electric race car set.
• Most variable resistors are designed so that by turning a dial or sliding a switch, you change the
amount of conducting material the current has to go through.
• The more conducting material the current has to go through, the higher the resistance…
less material and the resistance is less.
