All About Variable Resistor

                All About Variable Resistor

• Variable Resistors are the resistors in which the resistance can be continually altered and is not definite.
•  A variable resistor has 3 terminals out of which 2 are connected to the ends of the track and a third terminal is connected to the wiper. 
• The motion of the wiper allows in increasing and decreasing resistance. 
• Potentiometer, Rheostat and Trim Pot. 
• A potentiometer is used to divide the voltage. 
• It consists of resistive element. 
• Two terminals connected to electric contacts at the ends and a wiper in between. 
• The wiper slides on the resistive element making electric contact. 
• Rheostat is the most common way of varying resistance. 
• A semicircular insulator is wound by a resistance wire and the wiper slides from one turn of the wire to the next. 
• Trimming potentiometers also known as Trim Pots are similar to potentiometers. 
• But instead of having a knob for adjusting voltage, they are mounted with a screw. 
• They are turned with a screw driver and used for few adjustments.

Applications of Variable Resistors: 

1. Rheostat is used in power control devices like Light Bulb. 
2. Potentiometer is used in audio volume in A/V circuits, measurement of angles and tuning of circuits. 
3. Trim Pot is used in calibrating instruments, A/V circuits. 

Comparison between Fixed and Variable Resistors 

1. Fixed Resistors are resistors with a definite resistance value whereas Variable resistors vary in resistance either manually or automatic. 
2. Fixed resistors are either made up of carbon film, metal foil or wound wire whereas Variable resistors are made up of carbon composition, cermet(ceramic and metal), conductive plastic, wire wound. 
3. Fixed Resistors are used to prevent excessive current in the circuit whereas variable resistors are used to adjust volume and gain controls in the circuit.