Sunday 9 November 2014

RESISTOR ARTICLE

RESISTOR


Hello everybody Today our article is about RESISTOR in this article we will Discuss that how it works and how to read it color coding.



INTRODUCTION :


Resistor is an electrical component that is use to reduces the electric current. The ability to reduce current is known as Resistance and is measure in unit of ohm (symbol Ω ).

Resistors may be fixed or variable
both controlling the flow of current differently.

resistor is a passive two-terminal electrical component that implements electrical resistance as a circuit element. Resistors act to reduce current flow, and, at the same time, act to lower voltage levels within circuits.(source wikipedia)

A resistor is an electrical segment that cutoff points or controls the stream of electrical present in an electronic circuit. Resistors can likewise be utilized to give a particular voltage to a dynamic gadget, for example, a transistor.




SYMBOL :

resistor symbolResistor Resistor reduces the current flow.
resistor symbolResistor
potentiomemer symbolPotentiometer Adjustable resistor - has 3 terminals.
potentiometer symbolPotentiometer 
variable resistor symbolVariable Resistor / Rheostat Adjustable resistor - has 2 terminals.
variable resistor symbolVariable Resistor / Rheostat 
Trimmer ResistorPresest resistor
ThermistorThermal resistor - change resistance when temperature changes
Photoresistor / Light dependent resistor (LDR)Changes resistance according to light

some old and new symbol of resistor 



The symbol used in schematic and electrical drawings for a Resistor can either be a “zig-zag” type line or a rectangular box.

RESISTOR MADE UP OF:


The resistor is made up of following methods:

CARBON RESISTOR: 

  •  It is made up of carban or graphite paste.






  • FILM AND CERMET RESISTOR: 
It made up of conductive metal oxide paste.



  • WIRE WOUND RESISTOR :

  • Another type of resistor, called a Wirewound Resistor, is made by winding a thin metal alloy wire (Nichrome) or similar wire onto an insulating ceramic former in the form of a spiral helix similar to the film resistor above.

OHM LAW:


The current through in resistor is inversely proportional to its resistance and directly proportional to the voltage across it. Well it is known as OHM LAW.
OR
The resistor current C is equal to the voltage  V accross it and divided by its resistance R

mathematically it is written as:

The resistor's power consumption P   is equal to the resistor's current
times the resistor's voltage V :
P = I × V

The resistor's power consumption P  is equal to the square value of the resistor's current
times the resistor's resistance R :
P = I 2 × R

The resistor's power consumption P  is equal to the square value of the resistor's voltage V 
divided by the resistor's resistance R :
P = V 2 R

Rtotal  (EQUIVALENT RESISTANCE) MEASURE :

Resistors in parallel

The total equivalent resistance of resistors in parallel RTotal is given by:

So when you add resistors in parallel, the total resistance is decreased.

Resistors in series

The total equivalent resistance of resistors in series Rtotal is the sum of the resistance values:
Rtotal = R1R2R3+...

So when you add resistors in series, the total resistance is increased.

RESISTOR COLOR CODE:


The resistance of resistor and its tolerance are marked on resistor with color code band which is donoted by its value.
There are 3 types of color codes:
  • 4 bands: digit, digit , multiplier, tolerance.
  • 5 bands: digit, digit, digit , multiplier, tolerance.
  • 6 bands: digit, digit, digit , multiplier, tolerance, temperature coefficient.
1st Digit2nd Digit3rd DigitMultiplierToleranceTemperature Coefficient
4bands1234
5bands12345
6bands123456
Black000×100
Brown111×101±1%100 ppm/ºK
Red222×102±2%50 ppm/ºK
Orange333×10315 ppm/ºK
Yellow444×10425 ppm/ºK
Green555×105±0.5%
Blue666×106±0.25%10 ppm/ºK
Violet777×107±0.1%5 ppm/ºK
Grey888×108±0.05%
White999×109
Silver×10-2±10%
Gold×10-1±5%
None±20%

Resistance calculation of 4 bands resistor

R = (10×digit1+digit2multiplier

Resistance calculation of 5 or 6 bands resistor

R = (100×digit1+10×digit2+digit3multiplier


TYPES OF RESISTOR :

Variable resistorVariable resistor has an adjustable resistance (2 terminals)
PotentiometerPotentiometer has an adjustable resistance (3 terminals)
Photo-resistorReduces resistance when exposed to light
Power resistorPower resistor is used for high power circuits and has large dimensions.
Surface mount
(SMT/SMD) resistor
SMT/SMD resistors have small dimensions. The resistors are surface mounted on the printed circuit board (PCB), this method is fast and requires small board area.
Resistor networkResistor network is a chip that contains several resistors with similar or different values.

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