Good for you. It is impossible to tell the resistance of a resistor, just from the physical size.
There are two distinct types of resistors. They are metallic and nonmetallic. Metallic or metal resistors
are usually made of a metal conductor wound around a tube of insulative material. They are often called wire-
wound resistors. Metallic or wire-wound resistors generally are used when an extremely accurate amount of
resistance is required and/or when there is to be a high power requirement. Below are examples of wire-wound
Nonmetallic resistors are usually made of a mixture of carbon and clay. The most common method of
construction for nonmetallic resistors results in what is called the axial-lead resistor. A mixture of carbon and
clay is pressed inside a tube of insulating material. The wires are bonded to each end of the carbon-clay mixture
and the ends of the tube are sealed. Below is an example of an axial-lead resistor.
The two types of resistors are
metallic and wire-wound.
axial-lead and nonmetallic.
metallic and nonmetallic.