Introduction: What Is a Resistor ?
The Resistor is a passive electric component to create resistance in the flow of electric current . In all electrical circuits we can come across resistors .
- The resistance of the resistor is measured in Ohms .
- It occurs when a current passes throught a resistor across its terminal with a one volt drop .
- Resistance is calculate by using Ohm's law .
Step 1: OHM'S LAW
Ohm's law deals with the relationship between current and voltage in an idea conductor . Ohm's law states that electric current is directly proportional to voltage and inversely proportional to the current .
Ohm's Law is given by:
V = I R
where V is the potential difference between two points which include a resistance R. I is the current flowing through the resistance.
Step 2: TYPES OF RESISTORS
Resistors are classified into
- Carbon Resistors
- Film Resistors
- Wirewound Resistors
Carbon Resistor :
Carbon Resistors are the most common type of Composition Resistors . Carbon resistors
are a cheap general purpose resistor used in electrical and electronic circuits. Their resistive element is manufactured from a mixture of finely ground carbon dust or graphite and a non-conducting ceramic powder to bind it all together.
The Carbon Composite Resistor is a low to medium type power resistor which has a low inductance making them ideal for high frequency applications but they can also suffer from noise and stability when hot.
Carbon composite resistors are generally prefixed with a “CR” notation .
Film Resistor :
The generic term “Film Resistor” consist of Metal Film, Carbon Film and Metal Oxide Film resistor types, which are generally made by depositing pure metals, such as nickel, or an oxide film, such as tin-oxide, onto an insulating ceramic rod or substrate.
The resistive value of the resistor is controlled by increasing the desired thickness of the deposited film giving them the names of either “thick-film resistors” or “thin-film resistors”.
Metal Film Resistors have much better temperature stability than their carbon equivalents, lower noise and are generally better for high frequency or radio frequency applications. Metal Oxide Resistors have better high surge current capability with a much higher temperature rating than the equivalent metal film resistors.
Wirewound Resistor :
Another type of resistor, called a Wirewound Resistor, is made by winding a thin metal alloy wire (Nichrome) or similar wire onto an insulating ceramic former in the form of a spiral helix similar to the film resistor .
These types of resistor are generally only available in very low ohmic high precision values (from 0.01 to 100kΩ) due to the gauge of the wire and number of turns possible on the former making them ideal for use in measuring circuits and Whetstone bridge type applications.
Wirewound resistor types are prefixed with a “WH” or “W” notation and are available in the WH aluminium clad package or the W vitreous enamelled package with power ratings from 1W to 300W or more.