Thursday, July 14, 2011

resistance


                  Resistance
 A third factor that plays a role in an electrical circuit is resistance
All material impedes the flow of electrical current to some extent
The amount of resistance depends upon composition length, cross-section and temperature of the resistive material. As a rule of thumb, resistance of a conductor increases with an increase of length or a decrease of cross-section Resistance is designated by the symbol “R”. The unit of measurement for resistance is ohms (Ω).
 
 
          
            Resistance Circuit Symbols
Resistance is usually indicated symbolically on an electrical
drawing by one of two ways. An unfilled rectangle is commonly
used. A zigzag line may also be used

         types of resistance
  1-fixed resistance
  2- variable resistance
fixed resistance
it has constant  amount of resistive
  some figure of fixed resistor
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Measuring Resistance

Resistor Color Codes

variable resistors
we can change the value of resistance
some figure of variable resistors
 

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