Basic knowledge of Resister

Basic knowledge of Resister

Here present the article about the basic knowledge of Resister.

Defination:

A Resistor is defined as the passive electrical component with the primary function to limit the flow of electric current.


The formula for resistance is given by:
       R = ρl/A
where ρ is resistivity.
             l is length and A is area of cross section.
Resistance is measured in "ohm" (Ω.)
Resistor symbol:

 Different value resistors can be manufactured by changing the length and area of cross section or the material itself which changes the resistivity.

Materials generally used for fabrication of resistors are Nichrome(80 %  Ni and 20% Cr) , constantan(55% Cu and 45%Ni) and Manganin(85 % Cu and 10 % Mn and<5 %Ni).Metals are not used as they have a very high temperature coefficient of resistance.

Three main methods of fabrication are

1.  a slab or a rod of suitable resistivity,
2. Material using thinner cross section and longer length. The length is doubled and then wound in  such a way that inductance effects are cancelled out.
3. Thin films of material on insulating substrate. Each resistor has a current carrying capacity.     Current more than the prescribed wattage may damage the resistor.

The first two bands near an end indicate first 2 digits, digit corresponding to 3rd band is the power of 10 to be multiplied and fourth band indicates tolerance.
where brown = 1, black = O, red = 2 and silver = 10 % toterance.

 Hence its value is

             10 × 102  = 1 k Ω.

⇒how to calculate equivalent resistance in series and parallel 

   1.  series connection

       R= R1 + R2 + R3 + ………+ Rn

   2. paralllel connection

      1/R = 1/R1 + 1/R2 + 1/R3 +...…+ 1/Rn

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