Classification of Materials in Terms of Resistivity

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When electrons flow through any conductor determines its electric current. The resistivity of the substance determines this quality. A basic electrical property called resistivity calculates how strongly a substance resists the flow of electricity.
Materials are generally categorised as conductors, semiconductors and insulators based on the degree of their resistivity. The electrical behaviour of materials, how they are used in different electrical and electronic circuits is made easier by this classification.

Concept of Resistivity

Resistance (R) of a material depends on its dimensions and nature. It is given by Ohm’s law as:
R = ρ L / A
Where
* ( R ) = resistance (ohm, Ω)
* (ρ)  = resistivity (ohm-meter, Ω·m)
* ( L ) = length of conductor (meter)
* ( A ) = cross-sectional area (m²)

Classification of Materials in Terms of Resistivity

Resistivity (ρ) is the fundamental property of the material that determines how much the material resists the current flow, independent of its shape and size.
A substance is said to be a good conductor if its resistivity is low, allowing electrons to move freely. The substance acts as an insulator and opposes current flow if the resistivity is extremely high. Semiconductors are those with intermediate resistivity levels.

Classification of Materials Based on Resistivity

Conductors
Conductors are materials that allow electric current to pass through them easily due to the presence of a large number of free electrons. Their resistivity lies in the range of 10⁻⁸ to 10⁻⁶ Ω·m.
Examples: Copper, Silver, Aluminium, Gold, Iron, etc.
Classification of Materials in Terms of Resistivity-Gold
Gold

Properties:

* They have low resistivity and high conductivity.
* The conduction is mainly due to the movement of free electrons in the metal network.
* Resistivity of conductors increases with temperature, as thermal vibrations hamper electron movement.

Applications:

* Used in electrical wiring, transmission cables, and electronic circuits.
* Copper and aluminium are commonly used due to their balance between conductivity, cost, and strength.

Semiconductors

Semiconductors are materials whose resistivity lies between that of conductors and insulators, typically in the range of 10⁻⁵ to 10³ Ω·m. Their conductivity is moderate and can be controlled by temperature, impurities (doping) and light.
Examples: Silicon (Si), Germanium (Ge), Gallium Arsenide (GaAs).

Properties:

* There are no free charge carriers at absolute zero temperature, semiconductors act as insulators.
* Doping with impurities alters the amount of charge carriers, creating n-type or p-type semiconductors.
* Conductivity increases as the temperature rises because electrons gain energy and migrate to the conduction band.
As the temperature rises, resistivity falls, resulting in a negative temperature coefficient of resistance.

Applications:

* Widely utilised in integrated circuits, solar cells, diodes and transistors. They serve as the foundation for the contemporary computing and electronics sectors.

Insulators

Insulators are substances with nearly no free electrons that make it difficult for electric current to flow through them. They have a very high resistivity, often between 10⁸ and 10¹⁶ Ω•m.
Examples: Rubber, Plastic, Glass, Wood, Mica, and Ceramics.

Properties:

* It has very low conductivity and high resistance. There is a significant energy gap (e.g. > 5 eV) between the conduction and valence bands, which are empty and fully filled, respectively.
* It has very few electrons acquire sufficient energy to overcome the band gap, even at high temperatures. As the temperature rises, resistivity somewhat drops but stays high overall.

Applications:

Electric wires and cables are insulated with this material, which is crucial for stopping leakage currents and shielding circuits from shocks or short circuits. act as capacitor dielectric materials.

Comparative Summary

Property
Conductors
Semiconductors
Insulators 

Resistivity (Ω·m)

10⁻⁸ –10⁻⁶

10⁻⁵ – 10³ 

10⁸ – 10¹⁶  

Conductivity

Very high  

Moderate

Very low     

Temperature Coefficient

Positive

Negative

Slightly negative

Energy Band Gap (eV) 

~0

0.5 – 3   

>5

Examples

Cu, Al, Ag 

Si, Ge

Glass Rubber

Importance of Resistivity Classification

Resistivity is vital for designing electrical and electronic systems:
* It assists in anticipating how materials will perform under various environmental conditions, such as temperature and voltage, and in choosing the right materials for conductors, resistors and insulators. It is essential for creating contemporary semiconducting devices with effective current flow control.

Conclusion

A basic grip of how various substances conduct electricity can be gained by classifying materials according to their resistivity. The three foundational elements of electrical engineering and electronics are conductors, semiconductors and insulators. Current flow is made possible by conductors, stopped by insulators and precisely controlled by semiconductors.
Resistivity (ρ) is the essential property of a material that measures its opposition to the flow of electric current. It depends only on the nature of the material and not on its shape or size. Mathematically,
R = ρ L / A
Where R is resistance, L is length, and A is cross-sectional area.
 
Materials are classified into three categories based on resistivity:
Conductors – Low resistivity (10⁻⁸ to 10⁻⁶ Ω·m)
Semiconductors – Moderate resistivity (10⁻⁵ to 10³ Ω·m)
Insulators – Very high resistivity (10⁸ to 10¹⁶ Ω·m)
 
Many free electrons that flow freely via the material’s network structure are found in conductors. These electrons have a low resistivity value because they need very little energy to conduct current.
 
Because atomic vibrations impede electron passage, resistance rises with temperature for conductors. As more electrons in semiconductors acquire energy and migrate to the conduction band, resistance falls with temperature. Resistivity for insulators is still very high, although it may somewhat drop with temperature.
 
* Conductors: Copper (Cu), Silver (Ag), Aluminium (Al).
* Semiconductors: Silicon (Si), Germanium (Ge), Gallium Arsenide (GaAs).
* Insulators: Rubber, Glass, Plastic, Mica.
 
The main difference lies in their energy band gap (Eg).
* Because of the narrow band gap (0.5–3 eV) in semiconductors, electrons can move from the valence band to the conduction band with little energy.

* Insulators are poor electrical conductors because of their large band gap (>5 eV), which restrain electron mobility.
 
Studying resistivity helps in selecting suitable materials for different electrical and electronic applications:
Transmission and wiring are done with conductors. Electronic parts like transistors and diodes are made of semiconductors. Insulators are employed in electrical systems to guarantee safety and stop current leaks.

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