Resistors
Resistors are a very common component found in electronic circuits. From previous lessons, the unit of measure for resistance is the Ohm, represented by the Greek letter omega Ω. Resistors perform two functions in circuits. They limit the current flow through a circuit and they also can be used as voltage dividers.
There are several different types of resistors.
Fixed Resistors:
Composition Carbon Resistors - a very common type of resistor because they are inexpensive and readily available.
Metal Film Resistors - made by applying a metal film to a ceramic rod in a vacuum. The type of metal film being used and the thickness of the film determine the resistance.
Carbon Film Resistors – this type of resistor is made by coating a ceramic rod as well, only with carbon that is. Less expensive than metal film resistor and can have a higher tolerance rating than composition carbon resistors.
Metal Glaze Resistors – similar to the metal film resistor. This resistor is made by combining metal with glass, which is then glazed on to a ceramic base as a thick film. The amount of metal used determines the resistance.
Wire Wound Resistors – these are made by winding a resistive wire around a ceramic core several times. The resistance varies due to three factors: 1. Type of material of the resistive wire being used. 2. The diameter of the wire being used. 3. The length of the wire.
Resistors can often be determined by color code. Resistors usually have color bands used to determine the resistance value, the tolerance, and sometimes the reliability. The color bands on a resistor represent a different number. The chart below lists the numbers assigned to each color band of the resistor.
