The resistor is a two-terminal electrical component which implements electrical resistance in a circuit. On a broad level electrical resistors are divided into two categories: Fixed resistors and variable resistors. As the name implies a fixed resistor is the one which exhibits essentially constant value of resistance, whereas a variable resistor is the one whose resistance varies. Given below is the list of top 10 types of resistors used in Electrical and Electronic components:
Carbon film resistors
Carbon film resistors consist of carbon film over the ceramic cylinder. Such resistors are usually available in wattage ratings of 1/4, 1/2, 1 W with a tolerance value of 5%. The figure below displays a 22 ohms carbon film resistor having a tolerance value of 5%.
Metal Film Resistors
Metal film resistors have their external film made from nickel, chromium, constantum, manganin or from some other metal. Such resistors are also available is wattage ratings of 1/4, 1/2, 1 W. However they have a tolerance value of 1% and are recommended in applications which require high precision. The figure below displays 1K ohm, 1/2 watt resistor having a tolerance value of 1%.
Wire Wound Resistor
Wire-wound resistors are made of metal alloy that is wound around hollow porcelain core covered with a porcelain seal. Such resistors are designed to dissipate large quantities of heat and are rated for high wattage. The figure below displays a 50 watt, 25 ohms resistor with a tolerance value of 5%.
Integrated Circuit Resistors
Integrated resistors contain an array of resistors that is packed inside a single IC. Such resistors are used in circuits. Such resistors have low wattage rating and recommended where circuit power dissipation is low as well as where space is confined. The figure below displays a resistor IC.
Potentiometer
A potentiometer is a three-terminal variable resistor which provides variable resistance. Figure below displays a 100k ohm potentiometer.
Trimpot
Trimpot or trimmer potentiometer is a small potentiometer which is used for adjustment and calibration in circuits. Trimpots can be directly mounted on circuit boards and can be adjusted using screwdrivers.
SMD
SMDs or surface mounted resistors are factory built into various electronic and electrical devices. Figure below displays SMD resistor that can be assorted in PCBs.
Thermistor
A thermistor is a two-terminal variable resistor whose resistance changes with the change in temperature. The figure below displays an NTC thermistor.
Photoresistor
Photoresistor or Photoconductive cell is also a two-terminal resistor whose resistance changes with the amount of light falling on it.
Varistor
A varistor is a two-terminal variable resistor whose resistance is very high when the applied voltage is less than the breakdown voltage. However, when the voltage across varistor exceeds the rated voltage, its resistance becomes very small. Figure below displays a varistor:
