RESISTORS

RESISTOR

Resistor is an electronics component which resist or limit or oppose the flow of electrons through it. Resistors are used in almost every electronics circuits. This opposition to the flow of electrons hence to flow of electricity is known as resistance.

SYMBOLS:

The symbol of the resistor in an electrical or electronics circuits is an zig-zag line as shown in figure below.

Fig. Symbol of  Resistor

RELATION BETWEEN VOLTAGE, CURRENT AND RESISTANCE:

The relation between Voltage, Current and Resistance of the resistor is given by Ohm's law.

Ohm's law state that current through a close circuit is directly proportional to the voltage applied across it. Mathematically it can be written as,

                                                                   V ∝  I 

                                   or          V  = IR

where,

             V= Applied voltage.

              I = Current in the circuit.

             R= Resistance (proportionality constant).

UNIT OF RESISTANCE:

The unit of resistance is ohm (Ω). The resistance of the conductor is said to be 1 Ohm, if current through the conductor is 1 Ampere when 1 Volt of potential is applied across it. Ohm is the S.I. unit of resistance.

TYPES OF RESISTORS:

There are basically three types of resistors: i) Fixed resistors.

                                                                     ii) Variable resistors.                                                                                                                                 iii) Dependent resistors.

Fixed resistors:

Fixed resistors has fixed value of resistance. Its resistance value cannot be changed. It is most commonly used resistors. The picture below shows the fixed resistor.

Variable resistors:

Variable resistors are the resistors whose resistance value can be changed or varied. They have adjustable resistance value. The picture below shows the variable resistor.

Dependent resistors:

Dependable resistors are the resistors whose resistance value depends on the physical quantities such as light temperature or voltage. Example of dependent resistors are thermistor, photo resister, varistor, magneto,etc. The picture below shows the dependent resistor.

CALCULATION OF RESISTANCE USING COLOR CODE:

The resistance value of a resistance is written on the body of the resistance using color bands. Basically there are four band which decide the resistance value and the fifth band which determine the tolerance. The code is given in the figure below.

The color of the 1st, 2nd, 3rd band represent the numeric value and color of the 4th band specify the power of  tenth multiplier. The color of fifth band specify the tolerance. 

Let us take an example to understand how this work.

Let the color of 1st band be orange, 2nd band be brown, 3rd be red & 4th be silver.

Therefore the resistance will be:

           ORANGE - 3 , BROWN - 1, RED - 100, SILVER= ± 10%

Hence resistance is 3100 ± 10% Ω.

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