Carbon composition resistors are very small in size and have less power loss. Also, the resistors can have a very high value even up to few megaohms. These are so small that we cannot even indicate the value with readable digits on it. For that, we use colour codes on the resistor body to indicate the resistance value.
Construction of Carbon Composition Resistors
The main conductive part of a carbon composition resistor is made of carbon clay and leads are made of tinned copper. It is enclosed in a plastic or ceramic case to protect it from moisture and duct. It normally has diameters less than 10 mm. For higher power dissipation the size of the resistor should be increased. The shape of the resistor is of a cylindrical type.
There are two types of colour coding are used in carbon composition resistor and they are
- General Color Coding.
- Precision Color Coding.
The general colour coding has four colour bands and it is used in general purpose resistors that have the tolerance of ± 5% or more. Here, the first two colour bands represent the numeric part of the resistance value. The third band is the multiplier. For tolerance, the fourth band is used.
The precision colour coding has five colour bands to indicate the resistor value. The only difference from the general colour coding is that here the first three colour bands indicate the numeric value, the fourth band indicates the multiplier and the last colour band indicates the tolerance. The precision colour coding is used where tolerance is less than ± 2%.
Advantages of Carbon Resistors
- They are cheap.
- They have small size.
Disadvantages of Carbon Resistors
- They are noisy.
- They are very sensitive to temperature changes.
- The power dissipation capacity is small.
The carbon resistor is very widely used in general purpose electronic circuits due to their small size. As electronic circuits require very small currents, carbon composition resistors are suitable and safe. Because of so many drawbacks, these resistors cannot be used in all types of electric circuits but due to their low cost and small size, they are very popular.