Table of contents  
Resistivity of Materials  
Resistor ColourCoding  
Electrical Resistance v/s Electrical Resistivity  
Temperature Dependence of Resistance  
Temperature Dependence of Resistivity 
We know there are three types of materials; conductors, semiconductors and insulators. Conductors are the materials that can pass electricity through them. In this document, before we learn about electrical resistivity, let us know what is meant by electrical conductivity and its units.
Electrical Conductivity is an intrinsic property of a material which is defined as the measure of the amount of electrical current a material can carry. Electrical conductivity is also known as specific conductance, and the SI unit is Siemens per meter (S/m). It is also defined as the ratio of the current density to the electric field strength. It is represented by the Greek letter σ.
Electrical conductivity is a measure of how readily a material transmits an electrical current.
Electrical resistivity is the reciprocal of electrical conductivity. It is the measure of the ability of a material to oppose the flow of current.
The table below lists the electrical resistivity of several conductors, semiconductors, and insulators.
Electrical Resistivity of Different Materials
Materials having electric field and current density will have the following resistivity formula:
Where,
Conductors with a uniform crosssection and uniform flow of electric current will have the following resistivity formula:
Where,
Following is the unit of resistivity:
CGS unit  Ω.cm 
SI unit  Ω.m 
Dimension of resistivity M^{1}L^{3}T^{3}A^{2}
Following are the factors that determine the resistivity of materials:
Resistors are used in electrical circuits to control or reduce the flow of current in the circuit. Their resistance is indicated by using electronic color codes. Different color bands or rings are marked on these resistors for different values of resistance.
Resistor Colour Code and
Resistor Tolerance explained Highlights of the resistor colorcoding are as follows:
Let us take an example to understand resistor color coding.
Resistor Color Coding
Have you ever wondered why electrical appliances heat up when used for a longer time? Resistance is a property of an electric circuit or part of a circuit that transforms electric energy into heat energy in opposing electric current. In this document, we will study about such properties as resistance and Resistivity and the effect of temperature on these in detail.
Resistance
Resistivity
Difference between Resistance & Resistivity
In simple terms, resistance behaves differently with temperature for different materials.
However, there isn't a straightforward math formula that can describe how resistance changes with temperature for various materials, and it varies from one material to another.
When we increase the temperature, as a result the resistance increases. Suppose the resistance of a conductor at 0o C is R0 Ω increasing the temperature to C, the resistance becomes Rt Ω, as shown in fig.
Change in resistance =ΔR
ΔR = Rt  Ro
ΔR depends upon the following three factors:
1. ΔR is directly proportional to the initial resistance, Ro
2. ΔR is directly proportional to the rise in temperature, t_{0}C
3. ΔR depends upon the nature of the conductor.
Mathematically,
Where (α) is called the temperature coefficient of resistances. If the resistance of the material increases on increasing the temperature such materials have a positive temperature coefficient and when on increasing the temperature and the resistance decreases such materials have a negative temperature coefficient. From the equation, we can find
Example 1: Suppose you have a copper wire with a resistance of 10 ohms at 20 degrees Celsius. The temperature coefficient of resistance for copper is approximately 0.00393 /^{o}C. If the temperature increases to 50^{o}C, find the new resistance (Rt).
Solution: Substitute the values into the formula:
Rt =10Ω⋅(1+0.00393⋅(50−20))
Rt =10Ω⋅(1+0.00393⋅30)
R=10Ω⋅(1+0.1179)
R=10Ω⋅1.1179
R≈11.179Ω
So the new resistance Rt at 50^{o}C is 11.179Ω
Example 2: Let's say you have a sample of unknown material with a resistance of 20Ω at 25^{o}C and a resistance of 30Ω at 75^{o}C. Find the temperature coefficient of resistance (α) for this material.
Solution:
The formula for the temperature coefficient of resistance is given by:
So, the temperature coefficient of the material is 0.01 /^{o}C
The resistivity of a material is temperaturedependent. The temperature dependence of the resistivity is different for conductors, semiconductors, and insulators. Let’s discuss how resistivity varies in conductors and insulators before discussing semiconductors.
Energy Band Gaps in Materials
The resistivity of materials is dependent upon the temperature of the material.
ρ_{t} = ρ_{0} [1 + α (T – T_{0})]
is the equation that defines the connection between the temperature and the resistivity of a given material. In this equation ρ_{0} is the resistivity at an equilibrium temperature, ρ_{t} is the resistivity at t0 C, T_{0} is referred to as the reference temperature and α is the temperature coefficient of resistivity.
1. What is the SI unit of electrical resistivity?
SI unit of electrical resistivity is the ohmmeter.
2. What is the relationship between electrical conductivity and electrical resistivity?
The relationship between electrical conductivity and electrical resistivity is
σ = 1/ρ
3. Is rubber a good conductor of electricity?
Rubber cannot pass electricity, hence is not a conductor.
4. Explain the conductance of a semiconductor?
The conducting capacity of semiconductors lies between a conductor and an insulator.
5. Give some examples of good conductors?
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1. What is the relationship between resistivity and the color coding of resistors? 
2. How does the temperature dependence of resistance differ from the temperature dependence of resistivity? 
3. How can resistivity be calculated for a given material? 
4. What role does temperature play in the resistance of a material? 
5. How does the resistivity of a material affect its suitability for use in electrical components? 

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