Resistors are passive electronic components with high usage in electronic devices .

Principal characteristic of the resistors is resistance (opposition to current flow ) .Are many types of resistors :  for hard currents , for light currents , fixed value resistors , variable resistors and other types  .This types of resistors presented can be classify  by other parameters and manufactured process in many categories .

Main parameters of resistor are :

-tolerance t is noted in percents and represents the maximum accepted deviation of real resistance over the nominal value Rn  .

- dispersion power and nominal voltage Un represents the maximum electrical power  supported by the resistor .

Nominal standard power rating in watts for resistor are : .05, 0.1, 0.125, 0.25, 0.5., 1, 2, 4, 6,  12, 16, 25, 40, 50, 100W .

Usual the for a long life of the resistor the dispersed power from the circuit must be a ½ than nominal power .

Are many types of resistors and each type can be marked with a special standard symbol  .The main symbols of resistors can be viewed in the table bellow .

a: resistor , general symbol

b: resistor , tolerated symbol

c: resistor , un-standard  symbol

d: resistor with variable resistance

e: resistor with mobile contact

f: resistor with mobile contact and  stop position

g: potentiometer with mobile contact

h: potentiometer with mobile contact, general symbol

i: potentiometer with preset adjustment

j: two plugs resistor

k: shunt resistor

l: thermal resistor

m: thermistor general symbol

n: thermistor tolerated symbol

o: varistor general symbol

p: varistor tolerated symbol

The main parameters of the resistors can be marked using many methods like :

-color code marked on the body of the resistors with colored bands

- with letters

- with alphanumeric codes

Resistor Color Code Table

For decoding the color code of resistors we need to know how to interpret sowed in the table bellow

The first two colors market on the resistor body determinates the value of the resistor .

The third color marked on the resistor body represents the multiply coefficient

The fourth color band  represents the maximum resistor tolerance .

Resistors Letters code

Using the table bellow we can decode the value of the resistors coded ( marked ) with letters on the resistor body .

Resistors connection (Series, Parallel and Series-Parallel )

A resistor can be connected in a circuit in many types : series , parallel and mixt ( series and parallel connection  ).

If we connect two or more resistors together we obtain an equivalent resistance that depends of all resistors connected and the connection type used .

In series type connection all resistors are  connected end-to-end in a line to form a single path for electrons to flow .

If the resistor are connected in series , the equivalent resistance will be the sum of all resistors ( Re= R1+R2+..+Rn ) .

In the parallel connection all components are connected across each other’s leads , so in a purely parallel circuit, there are never more than two sets of electrically common points ( no matter how many components are connected ). There are many paths for electrons to flow (so each components have own flow current ), but only one voltage across all components .

So in this type of connection the equivalent resistance will be Re=(1/R1)+(1/R2)+…+(1/Rn).

In mixt (series-parallel ) connection you will need to calculate the equivalent resistance using the equivalent resistance formula for the series and parallel connection types .