A resistor is an electrical component that limits or regulates the flow of electrical current in an electronic circuit.
Resistance
It is the property of the material which opposes the flow of electric current through it.
A resistor is a passive component that limits or opposes the flow of electrical current in a circuit. In other word, resistor is an electrical or electronics component which exhibit the property called resistance.
Its unit is ohm and denoted by Ω (the Greek capital letter Omega).
Symbol
Classifications of Resistors
There are basically two types of resistors.
1) Fixed resistors
2) Variable resistors
Fixed Resistors
The value of fixed resistance is constant. Fixed resistors are classified into 4 types based on various factors like manufacturing style, resistance range, power rating etc.
The four types of fixed resistors are
1) Carbon composition
2) Carbon film
3) Metal film(again classified into thick film resistors and thin film resistors)
4) Wire wound(which consists of power style type and precision style type).
Variable resistors
The value of variable resistance can be changed (varied). They are used in electronic circuits to adjust the value of voltages and currents.
e.g. They are used in televisions as volume control, brightness control etc. There are three types of variable resistors. They are
1) Potentiometer (classified into carbon potentiometer and wire wound potentiometer)
2) Rheostat
3) Trimmer
Materials used for Resistors
The materials used for manufacturing the resistors are as follows
- Tungsten
- Bronze
- Nichrome
- Eureka
- Manganin
- Constentan
General Specification of Resistor
- Maximum voltage rating: The maximum voltage at which the resistor can operate without failure is called maximum voltage rating. This is also called Maximum operating voltage.
It is given by
Vmax= (power rating X resistance value)1/2
- Power rating: The maximum amount of heat dissipated by a resistor at maximum specified temperature without damage to resistor is called power rating of a resistor. It is expressed in Watt(W) at specified temperature.
- Temperature coefficient: The temperature coefficient of a resistor is defined as the percentage change in the resistance per unit change in temperature.
- Ohmic ranges: The ohmic ranges means the actual value of the resistance may be either larger or smaller than that of the indicated valueby the factor given by tolerance. The tolerance is defined as the accuracy to which the value of the resistor may be selected.
- Operating temperature: The maximum temperature at which the resistor can operate without failure is called maximum operating temperature. This is also called temperature rating.
