What is Resistor ?

Resistor is defined as a passive electrical component with two terminals that are used for either limiting or regulating the flow of electric current in electrical circuits. The main purpose of resistor is to reduce the current flow and to lower the voltage in any particular portion of the circuit.

    Electrons flow through materials when a pressure (called voltage in electronics) is placed on one end of the material forcing the electrons to “react” with each other until the ones on the other end of the material move out. Some materials hold on to their electrons more than others making it more difficult for the electrons to move. These materials have a higher resistance to the flow of electricity (called current in electronics) than the ones that allow electrons to move easily. Therefore, early experimenters called the materials insulators if they had very high resistance to electron flow and conductors if they had very little resistance to electron flow. Later materials that offered a medium amount of resistance were classified as semiconductors. 
    When a person designs a circuit in electronics, it is often necessary to limit the amount of electrons or current that will move through that circuit each second. This is similar to the way a faucet limits the amount of water that will enter a glass each second. It would be very difficult to fill a glass without breaking it if the faucet had only two states, wide open or off. By using the proper value of resistance in an electronic circuit designers can limit the pressure placed on a device and thus prevent it from being damaged or destroyed.

    The unit of measure for resistance is the ohm, which is represented by the Greek letter Ω. Before technology improved the process of manufacturing resistors, they were first made and then sorted. By sorting the values into groups that represented a 5% change in value, (resistor values are 10% apart), certain preferred values became the standard for the electronics industry.

    Resistors are marked by using different colored rings around their body. The first ring represents the first digit of the resistor’s value. The second ring represents the second digit of the resistor’s value. The third ring tells you the power of ten to multiply by. The final and fourth ring represents the tolerance. For example, gold is for 5% resistors and silver for 10% resistors. This means the value of the resistor is guaranteed to be within 5% or 10% of the value marked. The colors are used to represent the numbers from 0 to 9.

Types of Resistors:  

Resistor

There are two basic types of resistors as follows:

A) Linear resistors:

1) Fixed resistors

2) Variable resistors



Resistor symbol






B) Non-linear resistor:            

1) Thermistors

2) Varisters

3)Photoresistors