Resistivity of a Material: Overview, Questions, Preparation

Resistivity of a material can be denoted by the general formula: $R=\rho \frac{L}{A}$

Where,

R = Resistance

Ρ = Resistivity

L = Length of the Material

A = Cross Sectional Area

Here are some of the key factors that can affect the resistivity of the material

Temperature

In the case of conductors, resistivity is directly proportional to temperature. Similarly in the case of insulators or semiconductors, it will be inversely proportional to temperature.

Material

Conductors have low resistivity because the electrons move freely and collide with each other leading to high frequency reactions. But this cannot be possible in insulators due to tighter bonding. Hence insulators have low resistivity.

Presence of Impurities

More amount of impurities can lead to higher resistivity in the material because of more surface area.

Temperature Dependence on Resistivity is given by:

ρT​=ρ0​[1+α(T−T0​)]

The table given below will provide you a brief overview of some commonly used materials along with their resistivity’s:

Material	Type	Resistivity
Silver	Conductor	1.59×10−8
Copper	Conductor	1.68×10−8
Gold	Conductor	2.44×10−8
Aluminum	Conductor	2.82×10−8
Tungsten	Conductor	5.6×10−8
Iron	Conductor	1.0×10−7
Silicon	Semiconductor	6.4×102
Germanium	Semiconductor	4.6×10−1
Glass	Insulator	>10^10
Rubber	Insulator	>10^13

Materials can be classified into four main types on the basis of their resistivity. these are as follows:

1. Conductors:

• Materials that easily allow electric current to flow through them are known as conductors.
• Their resistivity depends on the temperature (directly proportional).
• Examples: Copper, Silver, Gold, Aluminum, etc.
• They can be used in electrical wiring or power transmission.

 

2. Insulators:

• Materials that do not allow electric current to pass through them are called insulators.
• These insulators have very high electrical resistivity.
• Examples: Rubber, Plastic, Wood, Glass, etc.
• They are used in designing of electrical insulation, circuit boards and safety equipments.

 

3. Semiconductors:

• Materials which are neither completely conductors nor insulators are called semiconductors. 
• They have a low to moderate electrical resistivity.
• Examples: Silicon, Germanium, etc.
• They are mostly used in sensors, solar cells, transistors, and digital electronic devices.

 

4. Superconductors:

• Material that show 0 electrical resistivity below a defined temperature are known as superconductors.
• Their electrical resistivity varies on the temperature.
• They are mostly used in MRI machines, Particle Accelerators, Quantum Computing, Maglev Trains, etc.
• Examples: Mercury, Nb, YBCO (Yttrium barium copper oxide) etc.