Resistors
De BISAWiki
A resistor is surely an electronics component that opposes the flow of electrons within an electrical circuit. There are several varieties of resistors available, along with a variety of resistance ratings, but generally each resistor will belong to one of two categories: fixed resistors and variable resistors. As the names indicate, fixed resistors have a fixed and unchangeable resistance value, while variable resistors have variable resistance values. What follows is a brief discussion of the numerous common kinds of fixed and variable resistors within the electronics world.
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Fixed resistors are discrete electronics components that are offered in a variety of resistance values and rated in Ohms. Common kinds of fixed resistors include carbon composition resistors, carbon film resistors, metal film resistors, wire wound resistors, and foil resistors. Each with the above kinds of fixed resistors has particular characteristics that suit that resistor type for particular purposes. For example, wire wound resistors generally can easily handle larger levels of power than, say, carbon composition resistors, but their wire coils often lead to unwanted inductive reactance in AC or RF circuits. Fixed resistors are often marked based on the conventional resistor color code.
Variable Resistors Variable resistors, because the name implies, are resistors whose resistance is able to be varied, whether manually or automatically. Common types of variable resistors include rheostats and potentiometers and in many cases are differentiated from one another by using the linearity of their variable resistance. For example, potentiometers are available in linear-taper varieties and logarithmic-taper varieties that differ inside the linearity of their variability as the potentiometer is turned. Potentiometers in many cases are low-Wattage devices, while rheostats in many cases are used for high-power applications in industrial electronics.
The choice between a fixed and variable resistor in circuit-design will be based upon whether one's circuit calls for resistance values or circuit characteristics that want variability or stability. For example, if your are constructing a radio receiver that'll be fixed using one radio frequency, a circuit that is composed entirely of fixed-value resistors along with other components will most likely suffice. If however, an example may be building a motor control circuit that requires variation in motor speed, a variable resistor would have been a more appropriate choice since a variable resistor could be used to vary the velocity of the motor. Thus there is a need for both fixed and variable resistors in electronics circuits, and a familiarity with both kinds of resistors is essential you are to have comprehensive knowledge of the various types of circuits that can call for resistors.
