What is a resister

Resistors:-

• Resistors are the most fundamental and commonly used component in all the electronic

circuits.

• The main function of a resistor within an electrical or electronic circuit is to oppose or

resist the flow of current, hence named as resistor.

• The symbol of resistor is shown in fig. below.

• Resistance is measured in units called “Ohm”.

Resistors can be broadly of two types :-

• Fixed Resistors.

Fixed Resistors :-

• A fixed resistor is one for which the value of its resistance is specified or fixed and

cannot be varied in general.

Example of fixed resistors are :-

Carbon Film Resistors : - These are made of carbon dust or graphite paste and

have low wattage values.

Metal Film Resistors :-These are made from conductive metal oxide

paste and have very low wattage values.

Wire wound resistors :- These resistors have metallic

bodies for heat sink mounting and have very high wattage ratings.

Carbon Film Resistors :-• This is the most general purpose, cheap resistor used

in electrical and electronic circuits.

• Heir resistive element is manufactured from a mixture of finely ground carbon dust

or graphite (similar to pencil lead) and a non-conducting ceramic (clay) powder to bind

it all together.

• The ratio of carbon dust to ceramic i.e. conductor to insulator, determines the overall

resistive value and the higher the ratio of carbon, the lower the overall resistance.

• The mixture is then moulded into a cylindrical shape with metal wires or leads

attached to each end to provide the electrical connection. Then finally it is coated with

an outer insulating material and colour coded markings to denote its resistive value.

• Usually the tolerance of the resistance value is ±5%.Such resistors with power ratings

of 1/8W, 1/4W and 1/2W are frequently used.

• The disadvantage of using carbon film resistors is that they tend to be electrically

noisy.