Resistor and its types

The Resistor is the basic elements in electronics since it oppose the flow os the current. Most of the application of electronics is depend on resistor only. The Resitance is the property of the substance which oppose the flow of the current passing it. The resistance is usually measured in ohms and it is represented by 'R'.

The value of resistance is found by the colour coding only. We can calculate the value by knowing its colour.The colour indicating table is below:

RESISTOR COLOR CHART
Color	1st Significant Digit	2nd Significant Digit	Number of zeros (multiplier)	Resistance Tolerance
Black	0	0	100	-
Brown	1	1	101	1%
Red	2	2	102	2%
Orange	3	3	103	-
Yellow	4	4	104	-
Green	5	5	105	0.5%
Blue	6	6	106	0.25%
Violet	7	7	107	0.1%
Grey	8	8	108	0.05%
White	9	9	109	-
Silver	-	-	10-2	10%
GOLD	-	-	10-1	5%

Types of Resistor:

1) Fixed Resistor

In an electrical circuit, some objects may need a lesser amount of current than the input value. In such cases, fixed resistors are used to reduce the flow of current. They are placed in such a way that a higher voltage must first pass through them before it flows further. The value of the resistance is fixed and does not change with change in the applied voltage or current flowing through it. The resistance value is measured in ohms and the value ranges from a few milliohms to about a giga-ohm.

Working of a fixed resistor:

 A fixed resistor has a resisting material in the center and conducting material at the end. Resistance is proportional to the length of the resistor and to the material's resistivity and inversely proportional to its cross-sectional area. The resistor will be damaged if it is exposed to a voltage greater than its maximum working value. The equation to determine the voltage V through a resistor of resistance R ohms with a current I in amperes is V= IR. 

Types of fixed resistors:

Based on the resisting material: carbon and metal oxide film, wire-wound, sand filled.

Based on their power ratings: 1/8, 20 watts, etc. 

Resistance value: ranges from a few milliohms to a giga-ohm. 

A tolerance of plus or minus 2 to 10% is usually given. 

Applications :

Resistors are universally used in all electrical circuits of devices like TVs, radios, refrigerators, machines, microelectronic semiconductor devices, regulators, etc.

Fixed resistors are further classified into

a) Carbon composition type resistors 

b) Metalized type resistors 

c) Wire wound type resistors

a) Carbon composition type resistors:

This is the most common type of low wattage resistor. The resistive material is of carbon-clay composition and the leads are made of tinned copper. These resistors are cheap and reliable and stability is high.

b)Wire wound resistors:

These resistors are a length of wire wound an insulating cylindrical core. Usually wires of material such as constantan (60% copper and 40% nickel) and manganin which have high resistivities and low temperature coefficients are employed. The completed wire wound resistor is coated with an insulating material such as baked enamel.

c) Metalized resistors
It is constructed using film deposition techniques of depositing a thick film of resistive material onto an insulating substrate.Only approximate values of resistance can be had by this method.

2) Variable Resistance

A variable resistor is a potentiometer with only two connecting wires instead of three. However, although the actual component is the same, it does a very different job. The pot allows us to control the potential passed through a circuit. The variable resistance lets us adjust the resistance between two points in a circuit.

For circuits requiring a resistance that can be adjusted while it remains connected in the circuit ( for eg:volume control on radio), variable resistors are required. They usually have 3 lead two fixed and one movable 

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