What is Resistance ?

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   Resistor is a fundamental passive element. The  resistor  is  a circuit  component whose principle  property is  to oppose  the flow of current  through  it . Resistance  is represented by the letter "R".

The symbol of the resistance is shown in below figure.
Units for resistance is shown in below figure
          A conductor is said to have resistance of  1  ohm , if   it  permits  one  Ampere   of current  to flow  through  it when  1 Volt is applied  across  it's  terminals.

                For conductors such as metals ,the resistance  is  very  low . This  is  due to the presence  of  free  electrons  in their atoms. For insulators  the  resistance  is very  high and for  semiconductors  the resistance lies in between that of metal and insulator.



       The resistance R of a conductor depends on the following factors .

 1) It is directly proportional to length of the conductor

 2) It is inversely proportional to area of cross section of the conductor

3) It depends on the nature of the material

Resistance of a conductor,
             
                        R = ρl/A

Here ,
 ρ=resistivity of the conductor
 l=length of the conductor
 A=area of cross section of the conductor

Resistivityis given by ,

                  ρ=RA/l
          Hence ,we define the resistivity as the resistance of a conductor of unit length and unit cross sectional area. The unit of resistivity is Ohm -Meter.

For colour coding of resistor click on below link 👇 :

http://electricalengineeringstudies.blogspot.com/2018/10/the-colour-code.html

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