How Does a Carbon Resistor Work? Key Principles & Applications
Resistors are a basic component compound found in electrical gadgets. Limitations in the passage current in a circuit are caused by resistors. A carbon resistor is known to be a fixed form of the resistor. Resistance per initially manufactured without coating. In the construction of carbon resistors, carbon films and metals over a ceramic career are used in bulk. Carbon resistors vary in physical sizes and their power dissipation limits range from 1 watt to ⅛ watts.
A carbon resistor is a fixed form of a resistor. The resistor has been in existence for over a hundred years. In the beginning, the resistors that were produced were without coating. The only type of available resistors was that of wire wound and carbon composition. The resistor is made of fine carbon fragments, with a binder in a cylindrical shape and baked with terminal lead at the opposite end are known as carbon resistors.
These carbon composition resistors are widely utilized in electrical circuits, and the majority of the resistors are made of metal or carbon films over a ceramic carrier. The most significant advantage of the carbon resistor is its ability to withhold high energy pulses. The carbon resistors' entire body conducts the energy for the electric current flowing through them. The carbon resistor is available in different physical sizes having a power dissipation limit from 1 watt down to ⅛ watt.
Carbon Resistor Definition
Many of the materials like nichrome, brass, platinum, and tungsten, which are metal, and alloys are used to produce the resistance. But most of these metals have low electrical resistance compared to carbon resistors, as it makes it difficult to produce high resistance without making the resistor bulky. It is already known that resistance is directly proportional to the product of the length and resistivity of the resistor. As the carbon resistor can produce a high accuracy value of resistance, it is usually used to calibrate the resistance. Carbon resistors are cheap, compact, and they can be directly added to the circuit boards like that of a tablet, mobile phones, and laptop processors. Due to all these practical purposes, they are more preferred as the metal wires are more expensive to produce compared to carbon, which is available in large quantities. Within the practical requirement, the resistance is reproduced by the carbon resistors.
Construction of Carbon Resistor
Though a variety of materials could construct carbon resistor, some parts of the carbon resistor are mentioned below
Ceramic core
Carbon film
Nickel Cap
Lead
Copper lead
Protective epoxy layer
The internal structure of the carbon resistor is shown in the below diagram. The carbon resistors are manufactured by using the deposition process. In this process, the carbon film is deposited upon the ceramic body of the resistor. The carbon film restricts the current flow, and as a result, it is an imperative part of the resistor. At a high temperature of 1000°C, hydrocarbons like methane or benzene are cracked. The ceramic mould acts as an insulator to the high temperature or electricity, and pure graphite (carbon) is used for distribution on the ceramic body. The presence of the carbon film makes the resistor withstand the electricity without any damage. The diagram below is the schematic construction of a carbon resistor.
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In the above figure, it is observed that the carbon film is in helical shape as it helps to accurately resist this carbon resistor. It also helps the effectiveness of the resistor with the decrease in the width and increase in the length. As mentioned earlier, resistance is directly proportional to the distance; the value of the resistor can also be altered by increasing or decreasing the length of the spiral carbon film. For the protection of the resistor, an epoxy coating is also provided. The end portion, as shown in the diagram, is made up of metal, and the connecting leads are made up of copper, which is joined to the metallic ends.
How Does a Carbon Resistor Work?
When people construct an electric or electronic circuit for a particular job, they need to induce the precise amount of resistance in the circuit board. It is achieved by adding the tiny components called the carbon resistor. These components are a little package of resistance that is wired into the circuit so that a precise amount can reduce the flow of current. The tolerance of resistors without being damaged is because of carbon coating. The resistor's efficiency is enhanced by an increase in length and decrease in width. The epoxy coating helps in the protection of resistors. In resistors the metals are used in the end part and copper is used for connecting leads.
A certain amount of resistance must be induced in the circuit board while building an electronic circuit which is implemented by using carbon resistors which are generally small components. These small components are connected to the circuit for resisting the floor to a certain amount. In carbon resistors, the carbon is deposited on a ceramic core and this deposition station is then etched in a spiral transforming it into a wire. For carbon and lead to make an excellent contact, nikle caps are connected to both ends.
What is the Symbol of Carbon Resistor?
In most of the electrical and electronic circuit diagrams, the most frequently used symbol is that of a zig-zag line for a resistor with the value of its resistance denoted by the Ohms. Fixed resistors usually have only one value of the resistance. Still, variable resistors can be provided with an infinite number of resistances, which may vary from zero to their maximum value. Notation is used for Carbon resistors as "CR" (CR10kΩ) and is available in E6(+20% tolerance(accuracy)), E12(+10% tolerance) and E24(+5% tolerance).
Carbon Resistor Symbol
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FAQs on Carbon Resistor: Complete Physics Guide
1. What is a carbon resistor and what is it made of?
A carbon resistor is a type of passive electronic component that is used to oppose or limit the flow of electric current in a circuit. It is constructed from a mixture of finely powdered carbon or graphite and a non-conductive ceramic or resin binder. The specific resistance value is determined by the ratio of carbon to the binder material. This mixture is then molded into a cylindrical shape and baked, with connecting leads embedded at each end.
2. How can you determine the resistance value of a carbon resistor using its colour code?
The resistance value of a carbon resistor is indicated by a set of coloured bands, typically four. To read the code:
The first band gives the first significant digit of the resistance value.
The second band gives the second significant digit.
The third band acts as the multiplier (the power of 10 to be multiplied by the first two digits).
The fourth band indicates the tolerance, which is the percentage accuracy of the resistor's value.
For example, a resistor with bands of Brown (1), Black (0), Red (x10²), and Gold (±5%) would have a resistance of 10 × 10² = 1000 Ω or 1 kΩ with a ±5% tolerance.
3. What are the common applications of carbon resistors in electronic circuits?
Due to their properties, carbon resistors are used in various electronic applications. Some common uses include:
Current Limiting: To protect sensitive components like LEDs from excessive current.
High-Voltage Power Supplies: For use in devices like X-ray machines and radar systems.
Surge Protection: Their ability to withstand high energy pulses makes them ideal for protecting circuits from voltage spikes.
High-Frequency Applications: They have low inductance, making them suitable for circuits where wire-wound resistors would be problematic.
Medical Equipment: Used in devices such as defibrillators to protect both the equipment and the patient.
4. Why is carbon a preferred material for making general-purpose resistors?
Carbon is preferred for making general-purpose resistors primarily due to its cost-effectiveness and electrical properties. Carbon is abundant and inexpensive to process. More importantly, carbon composition resistors are non-inductive. Unlike wire-wound resistors, which are essentially coils of wire and create significant inductance, carbon resistors do not store magnetic energy. This makes them ideal for high-frequency circuits where unwanted inductance can interfere with circuit performance.
5. How do carbon resistors differ from wire-wound resistors?
Carbon resistors and wire-wound resistors differ in their construction, properties, and applications:
Construction: Carbon resistors are made from a carbon-ceramic composite, while wire-wound resistors are made by winding a metal alloy wire around a core.
Power Rating: Carbon resistors typically have low power ratings (e.g., 1/8W to 2W), whereas wire-wound resistors are used for high-power applications.
Stability & Precision: Wire-wound resistors are much more stable with temperature and can be made with higher precision (lower tolerance). Carbon resistors are less stable and have higher tolerance values.
Inductance: Carbon resistors have very low inductance, making them suitable for high-frequency use. Wire-wound resistors have high inductance due to their coiled structure and are unsuitable for such applications.
6. What are the main advantages and disadvantages of using carbon composition resistors?
The primary advantages and disadvantages of carbon composition resistors are:
Advantages: They are inexpensive to manufacture, can withstand high-energy pulses without damage, and have very low inductance, making them excellent for high-frequency circuits.
Disadvantages: They have poor stability, as their resistance value can change significantly with temperature, age, and voltage. They also generate more electrical noise compared to other resistor types, which makes them unsuitable for sensitive audio or measurement circuits.
7. How does temperature affect the resistance of a carbon resistor?
Carbon resistors have a negative temperature coefficient (NTC) of resistance. This means that as the temperature of the resistor increases, its resistance value decreases. This is an important characteristic to consider in circuit design, as self-heating from current flow or changes in ambient temperature can cause the resistance to drift from its nominal value, potentially affecting the circuit's performance.
8. What does the tolerance band on a carbon resistor signify?
The tolerance band, which is the last coloured band on a carbon resistor, signifies the permissible deviation in its actual resistance value from its stated (or nominal) value. It is expressed as a percentage. For instance, a Gold band represents a ±5% tolerance, while a Silver band represents a ±10% tolerance. A 1000 Ω resistor with a 5% tolerance is guaranteed to have a resistance between 950 Ω and 1050 Ω.
9. What is the working principle of a carbon resistor?
The working principle of a carbon resistor is based on the inherent electrical resistivity of a composite material. It does not rely on the length and cross-section of a wire. Instead, it uses a bulk mixture of conductive carbon particles and a non-conductive binder. When voltage is applied, electrons must navigate a complex, resistive path through this mixture. The density and distribution of the carbon particles within the binder determine the overall opposition to current flow, thus establishing the resistor's specific resistance value.
