Carbon Resistor And Its Structure

Carbon resistor is one of the most common types of electronics used. They are made from a solid cylindrical resistive element with embedded wire leads or metal end caps. Carbon resistors come in different physical sizes with power dissipation limits commonly from 1 watt down to 1/8 watt.

What are Carbon Resistors?

There are many materials used to produce resistance particularly metals and alloys like nichrome, brass, platinum and tungsten alloys. However, most of these metals have low electrical resistivity, unlike carbon resistor, which makes it difficult to produce high resistances without becoming bulky. We already know that:

Resistance ∝ {Length ×Resistivity}

However, they can produce highly accurate values of resistance and hence are used usually to calibrate and compare resistances.

For most practical purposes, however, carbon resistors are preferred. This is because they are cheap to produce, compact and can be directly printed onto circuit boards (like the computer processors in phones and tablets). They also reproduce resistance fairly well within practical requirements. Compared to metal wires which are expensive to produce, carbon is abundantly available making it cheap. (Ask the price of a resistor in an electronic component store, you can get a dozen for just 2 rupees!).

Resistor

Resistor

Parts of a Carbon Resistor

Resistors can be constructed out of a variety of materials. The different parts of a carbon resistor are:

  • Ceramic Core
  • Nickel Cap
  • Lead
  • Carbon Film
  • Protective Lacquer

The internal structure of a carbon resistor is shown in the image below.

Parts of a Carbon Resistor  

Parts of a Carbon Resistor  

Uses of Carbon Resistors

The carbon resistor contains carbon coated onto a ceramic core. A spiral is etched on the deposited carbon which turns it into a wire wound on a ceramic core. Depending on the resistance required, pitch, diameter and length of the carbon spiral vary. Nickel caps are attached to both ends of the core so as to create a good contact between the carbon and lead. The leads are soldered onto the nickel caps and the entire resistor is coated with lacquer for electrical insulation.

For small resistances required for small currents, the metal caps act as heat sinks to carry away heat dissipated by the resistor. For larger current requirements, a metal heat sink is separately attached to carry away excess heat and to prevent the resistor from burning up.
Carbon resistors are specially colour-coded to identify the resistance.

You may also want to check out these topics given below!


To learn more on resistors like its dependence on temperature, the heating effect of current, resistors in series and parallel with the help of interactive video lessons download BYJU’S – The Learning App.

Frequently Asked Questions on Carbon Resistor

What is the use of thermistor?

It is used for the conversion of temperature into electric voltage.

What is the tolerance of gold colour resistance?

The tolerance of gold colour resistance is 5%.

What are the uses of rheostat?

The uses of rheostat are it can be used as a variable resistor as well as a potential divider.

What is the tolerance of silver strip?

The tolerance of the silver strip is ±10%.

What is the value of the resistor with colour bands brown, black and red?

The value of the resistor with colour bands brown, black and red is 1000 ohms.

Practise This Question

A glass of water at room temperature and a hot mug of coffee are placed on two tables inside a closed room. As the coffee cools down, what would happen to the temperature of the water?

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