Carbon Composition ResistorPublished on 24/2/2012 & updated on 28/8/2018
These are so small that we cannot even indicate the value. For that we use color codes.
Construction of Carbon ResistorsThey are made of carbon clay and leads are constructed of tinned copper. It is enclosed in plastic case so that there will be no entry of moisture and other harmful particles in the resistor. They have diameters less than 10 mm. For higher power dissipation the size of the resistor should be increased. The shape of the resistor is of cylindrical type.
Color Code of Carbon ResistorsThe color coding is provided since its size is too small and hence we cannot indicate the value of the resistor in the plate. The color code is as follows - There are two types of color codes that we use -
- General Color Coding.
- Precision Color Coding.
General Color CodingThey are used if it has four bands and also they are used in the case of general purpose resistor. They have tolerance of ±5% or more. To calculate resistance value, see the color of first digit and number it according to color code. Next, take the second color code and indicate the digit according to the color code. Third band is the multiplier band so put that the power of ten and multiply it with the previous number we got from the two digits, that will indicate the value and for tolerance see the fourth band and indicate the tolerance accordingly. For example, if a resistor has a color code of Brown, Grey, Brown and Gold then the first digit we get is 1 as the brown indicates the digit 1. Secondly the second band indicates the code to be 8. So the number we got from those two digits is 18. Third band indicates the multiplier the multiplier so the multiplier is 10 as brown indicates 1. Fourth band indicates the tolerance value, Gold has the tolerance of ± 5 %. So the resistance value we got is 180 ± 5 %.
Precision Color CodingIn this case we have five bands to indicate the resistor value. The first band is not black as in case of general purpose resistor. The only difference from the general resistors is that it has five bands and the first three will indicate the value, fourth one will indicate the multiplier and the last color indicates the tolerance value. They have the tolerance less than ± 2 %. So the color code is used accordingly.
Advantages of Carbon Resistors
- They are cheap.
- They have small size.
Disadvantages of Carbon Resistors
- They are noisy.
- The power dissipation capacity is small.
Conclusion The carbon resistor is very widely used in electronic circuits and integrated circuits due to their small size. They can be used to make electronic circuits because the circuits will require a very small current so the carbon resistor can handle safely. They are very sensitive to temperature changes. Also the small power handling capacity is the main drawback of these types of resistors. Also, these types of resistor tend to produce noise. Due to these they reasons they cannot be used in all the electric circuits but due to their low cost and small size, they are very popular.
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