October 28, 2008

What is Resistor?

One of the most important components in an electrical system is resistor. Resistor opposes or limits the flow of direct or alternating current. Resistor can divide and reduce the current and voltage and protect an electrical circuit.

The ability of the resistor to oppose or limit the flow of electric current in an electrical circuit is called resistance. When a voltage is applied to an electrical circuit, it causes the electrons to flow through the circuit. As electrons flow through an electrical circuit, it encounters materials (resistance) that hinder the electrons to flow. Those materials are provided by the resistor or any component in the circuit.

Resistors are designed to provide definite value of resistance. Resistors can be classified into two major categories; according to value and the material they are made of.

There are two types of resistor, according to value; the fixed and variable resistors. Fixed resistors provide only a single resistance value. Variable resistors can provide multiple resistances. A potentiometer is an example of variable resistor with three terminals, which is used to control voltage. Another example of variable resistor is rheostat which is used to control current.

Resistors can also be classified as carbon composition and wire wound resistor. Carbon composition resistors are the most commonly used resistors in electronics and they are made in the standard resistor values. Wire wound resistors are often used in high current circuits.

A. carbon composition resistor with fixed resistance value,   B & C. potentiometer / variable resistor,   D. light dependent resistor (LDR), E. symbol for variable resistor      F. symbol for fixed resistor.