3 Apr 2019

What is Resistance and Resistor- Types of Resistors, Working Principle of Resistors and Ohm's Law

What is a Resistor 

A Resistor is a passive electronic component having two terminals, that limits the flow of electrons through a circuit. Passive components are the components that can only consume power (they cannot generate power).


Uses of Resistors

The main use of resistors is to reduce the flow of current in a circuit, but it is not limited to this only. Resistors find applications in various fields like-
*Resistors can be used to divide voltages (as voltage divider)
*To adjust signal levels
*Terminating transmission lines
*To bias active elements
*Timing and frequency applications
*In heating applications etc.


Types of Resistors

Resistors can broadly be categorized into two types-
*Fixed Resistors
*Variable Resistors

Fixed resistors

As clear by its name, fixed resistors cannot change it's value. 
The fixed resistors can again be classified into following three types-
*Carbon composition resistors
*Metalized resistors
*Wire wound resistors

Variable resistors

The resistance of variable resistors can be changed continually or can be set to a certain value as per the requirement.
On the basis of this the variable resistors can again be of two types- 
*The variable resistors that can change its value continually like that used in volume control applications and 
*The variable resistors that can be set to a fixed value as desired like in case of potentiometers (adjustable resistor).


Working Principle of resistor

Ohm's Law

For an ideal resistor the Ohm's law is given as -
According to Ohm's law the voltage (V) across a resistor is directly proportional to the current (I) flowing through it. Here the constant of proportionality is the resistance (R).
This relationship between voltage and current is given as-
V=IR


Unit of Resistance (R) and Conductance (G)

Unit of electrical resistance is Ohm (Ω) . Ohm is the SI unit of resistance. Other unit of resistance can be obtained from the Ohm's law.
By Ohm's law-
R=V/I
Therefore the unit of resistance is- Volt per Ampere or V/A.
Conductance (G) is opposite to the resistance. Conductance can be defined as the ease with which the current flows through a substance. Formerly the unit of conductance was mho (℧)(opposite of Ohm, the unit of resistance). The standard unit of conductance is siemens (S).

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