Electrical Resistance

Introduction:

Electrical Resistance is one such topic including the resistivity, factors affecting these two, their relation, etc. The opposition to current flow in an electrical circuit is measured by resistance (also known as ohmic resistance or electrical resistance). The Greek letter omega (Ω) is used to represent the SI unit of resistance which is ohms. The greater the resistance, the greater the impediment to current flow.

What is Electrical Resistance?

The sub-atomic configuration of any material reveals that it has free electrons that are in random movement. The application of potential difference across any material leads to the alignment of these charge carriers. Depending on the majority of the charge carriers, the direction of flow of current is established. However, it is the property of the material to restrict the flow of current through it that disturbs its original state. Hence, the material opposes the current.

A relation is observed between the potential difference applied across the conductor and the current passing through it. Let V be the potential difference and I be the current in the following circuit.

Then, Resistance R can be expressed by:

V ∝ I 

V = IR

V is expressed in volts

I is expressed in amperes

R is expressed in ohms

In terms of electrical resistance:

R = V/I

The SI unit of electrical resistance is one ohm. Hence, it is the measure of the easiness of the electric current passing through the conductor. The different materials have different resistance depending on multiple factors.

Depending on the value of resistances of different materials, these can be categorized as conductors, semiconductors, and insulators. The conductor offers the least resistance to the flow of current through them. Hence, are widely used in electrical appliances. Some of the popular conductors are copper, gold, silver, etc.

The insulators have the highest resistance to the flow of current. Thus, these are perfect for  applications that require protection from  electric charge conduction. Some of the popular insulators are wood, glass, etc.

The semiconductors have  a resistance that lies in between those of conductors and insulators. Hence, these observe both the characteristics of conductors and insulators. Some of the semiconductors are silicon, germanium, etc.

What are the factors affecting electrical resistance?

The electrical resistance is dependent on the following aspects of the conductor:

Length: The increase in the length of the conductor increases the electrical resistance of the material.

Cross-section: The increase in the cross-sectional area of the conductor decreases the resistance offered by the material to the current flow.

Material: The material of the conductor depends on the resistivity of the conductor and hence it is directly proportional to the material of the conductor.

Temperature: The increase in temperature of the material decreases the resistance of the material. This is because the  temperature rise imparts thermal energy to the electrons and hence it opposes the resistance.

What is resistivity?

It is defined as the electrical resistance offered per unit length and unit cross-sectional area at a specific temperature and is denoted by ρ. The SI unit of resistivity is ohms. meter. Its formula is:

=EJ

where,

ρ is the resistivity of the material and is expressed in Ω.m

E is the electric field and is expressed in V.m-1

J is the current density and is expressed in A.m-2

Some of the materials and their associated resistivity are:

•          Copper: 1.68×10−8
•          Wood: 1.00×1014
•          Teflon: 1.00×1023
•          Silver: 1.00×10−8
•          Air: 2.30×1016
•          Aluminum: 2.82×10−8

Conclusion:

Thus, we can conclude that in electrical circuits, resistance is a significant factor; higher resistance makes current flow more difficult, whereas lower resistance makes current flow easier. The electrical resistance of any material is a foundation stone for its use in multiple physics experiments and other applications.