Resistor and its brief explanation and its types

Resistor, Resistance, Symbol of Resistor 

                         A resistor is an electrical component that limits the flow of electrical current in an electronic circuit.

Resistance:

           Resistance is a measure of the opposition to current flow in an electrical circuit. Resistance is measured in ohms, symbolized by the Greek letter omega (Ω). The resistance of resistor is depends upon 3 factors: Resistivity of the material used (ρ), Length of the resistor (l), Cross section area of the resistor (A) and temperature (T).

Color Coding of Resistor 

                       Resistors are available in a range of different resistance values from fractions of an Ohm (Ω) to millions of Ohms.

Generally resistor values are printed onto the body of the resistor as numbers or letters when the resistors body is big enough to read the print, such as large power resistors but when the resistor is small, it uses colored painted bands to indicate their resistive value. These colored painted bands produce a system of identification generally known as a Resistors Color Code.

 The resistor color code markings are always read one band at a time starting from the left to the right, with the larger width tolerance band oriented to the right side indicating its tolerance. By matching the color of the first band with its associated number in the digit column of the color chart below the first digit is identified and this represents the first digit of the resistance value and again, by matching the color of the second band with its associated number in the digit column of the color chart we get the second digit of the resistance value and so on. Then the resistor color code is read from left to right as illustrated below:

To understand the resistor; please click the link below 

https://www.youtube.com/watch?v=GLD7AgAYqwA 

Types of Resistor 

                    There are many different types of Resistor available for the electronics constructor to choose from, from very small surface mount chip resistors up to large wire wound power resistors.

Fixed Resistors 

                     As the name tells everything, fixed resistor is a resistor which has a specific value and we can’t change the value of fixed resistors. 

Types of fixed resistors: 

                       1. Carbon Composition Resistors 

                       2. Carbon film Resistors 

                       3. Metal Film Resistors 

                       4. Wire wound Resistors

Carbon Composition Resistors: 

                           These resistors are cylindrical rods which are a mixture of carbon granules and powdered ceramic. The resistor value depends on the composition of the ceramic material. A higher quantity of ceramic content will result in more resistance. Since the rod is coated with an insulated material, there are chances of damage due to excessive heat caused by soldering.

Carbon film resistors: 

                          This resistor is formed by depositing a carbon film layer on an insulating substrate. Helical cuts are then made through the carbon film to trace a long and helical resistive path. The resistance can be varied by using different resistivity carbon material and modifying the shape of the resistor. The helical resistive path make these resistors highly inductive and of little use for RF applications.

Wire wound resistor: 

                             Another type of resistor, called a Wire wound 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 above. 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.

Metal Film resistor: 

                         These resistors are made from small rods of ceramic coated with metal (such as a nickel alloy) or metal oxide (such as tin oxide). The value of resistance is controlled mainly by the thickness of the coating layer (the thicker the layer, the lower is the value of resistance). A fine spiral groove can be cut along the rod using a laser to split the carbon or metal coating effectively into a long and spiral strip, which forms the resistor. 

Variable resistor: 

                  Presets and potentiometers are commonly used types of variable resistors. These are mostly used for voltage division and setting the sensitivity of sensors. These have a sliding contact or wiper which can be rotated with the help of a screw driver to change the resistance value. 

To understand the types of resistor; please click the link below 

https://www.youtube.com/watch?v=cz_zlNWRkFM

Factors affecting Resistance of Resistors

1. What it’s made of. Metals are good conductors so have lower resistance than an insulator of the same dimensions.

2. Length – the longer, the greater resistance. 

3. Area of cross section – the larger the lower. 

4. Temperature (metals: higher temperature = higher resistance because the vibration of the metal lattice impedes the drift of the electrons, semiconductors: like thermistors, resistance decreases with temperature) 

Specification of Resistor

Resistors are rated by the value of their resistance and the electrical power rating that they can safely dissipate based mainly upon their size.

The Resistor Power Rating is defined as the amount of heat that a resistive element can dissipate for an indefinite period of time without degrading its performance. Unit is given in watts (W). 

The voltage applied to and the current (A) running through a resistor determine the power (W) that needs dissipation. 

¼ watt is the typical rating for the basic electronics resistor. 

To understand the resistor power rating; please click the link below

 https://www.youtube.com/watch?v=tME40e7VLvk 

 Resistor in series and parallel

Comparison of Series and Parallel resistance Circuit

Applications of different types of resistors:

 Different types of resistor can be used in circuit based on the circuit nature. 

1. Carbon film resistors used in high voltage and temperature applications.

 Operating temperatures are up to 15kV with a nominal temperature of 350°C. 

 Examples are 

             High voltage power supplies 

             Radar

             X-rays

             Laser 

2. Metal Film Resistor applications: 

                  In circuits where tight tolerance, low temperature coefficient and low noise properties are important, often metal film resistors are used. Examples of applications are 

                  Active filters or bridge circuits 

3. Wire wound resistors applications: 

                Wire wound resistors are typically used in high power and industrial applications such as circuit breakers and fuses.