Types of Resistor

Resistors in ordinary use may be broadly sub-divided in to the following categories
(a) Ware wound resistor (b) compressed carbon resistors (c)carbon film resistors.This type of resistor are fixed    value can not change the value,but we can use the another type of resister is called variable resistor
The variable resistor perform 0 ohm to fixed value.For example on variable resistor value is 200 ohm we can change 0,1 ohm,2.......200 ohm.

variable Resistor

 

The variable resistor can change current and voltage depend on the connection.
The variable resistor we can use two way.
1. Rheostat.
2. potentiometer  or post.




Rheostat-Two terminals are used: one connected to an end of the track, the other to the moveable wiper. Turning the spindle changes the resistance between the two terminals from zero up to the maximum resistance.Rheostats are often used to vary current, for example to control the brightness of a lamp or the rate at which a capacitor charges.






Potentiometer- Variable resistors used as potentiometer have all three terminals connected.

This arrangement is normally used to vary voltage, for example to set the switching point of a circuit with a sensor, or control the volume (Loudness) in an amplifier circuit. If the terminals at the ends of the track are connected across the power supply then the wiper terminal will provide a voltage which can be varied from zero up to the maximum of the supply. 

And Another is the Preset-These are miniature versions of the standard variable resistor. They are designed to be mounted directly onto the circuit board and adjusted only when the circuit is built. For example to set the frequency of an alarm tone or the sensitivity of a light-sensitive circuit. A small screwdriver or similar tool is required to adjust presets.

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