ABSTRACT
This chapter discusses state the function of a resistor and explains the difference between a fixed-value and variable-value resistor. It also explains state the relationship between the physical size and power rating of a resistor and outlines the differences between a carbon-composition resistor, cracked-carbon resistor, metal-film resistor and wire-wound resistor. The chapter explores why resistors are manufactured in 'preferred values', and explain the significance of their 'E-numbers'. Carbon-composition resistors have been in use for over a hundred years and, together with wire-wound resistors, were the only types of resistor available until well into the 1960s. Wire-wound resistors are the oldest type of resistor and are manufactured from 'resistance wire'. Variable resistors are used when it is necessary to vary the value of the current in a circuit, or to vary the voltage across a circuit. All surface-mount resistors conform to a 3-digit or 4-digit code.
