Resistance and Resistivity

The study of physics includes a variety of properties, theories, and studies of various characteristics of motion. It is the study of galaxies, the entire universe, and even the tiniest of atomic particles. Resistance and resistivity are some of its properties. Generally, resistance is defined as an opposition to something. As a result of their similar names, many people become confused about the differences between the two properties. The study of electricity and magnetism relies heavily on resistance and resistivity. In this article, we are aiming to focus on resistivity and resistance and their major differences.

What is Resistance?

Resistance is the measure of a material’s ability to resist the flow of current. Currents flow through a conductor when a voltage is applied to it, and the free electrons of the conducting material begin to move in a specific direction. When these electrons collide with other atoms and molecules, heat is generated. In other words, resistance is the opposition that the current faces when it passes through a conductor.

According to Ohm’s law, which states that V = IR, R represents the constant that represents proportionality. This constant is known as the resistance of the conductor since we already know that V represents the potential difference and I represents the current. Due to the fact that resistance is also relevant in various other physics fields, we will focus on electrical resistance in particular. Resistance is measured in SI units called ohms (Ω), and one ohm is equal to one ampere of current passed through a conductor when there is a one-volt difference between the ends of the conductor. The expression for R based on Ohm’s law is:

Ohm’ law is,

V ∝ I

V = IR

Thus, R can be written as,

R = V/I

  1 ohm = 1 volt/1 ampere

R may also be expressed as follows when solved further,

R = ρ l/a

Where,

l is the length of the conductor

a is the cross-sectional area of the conductor

ρ is the resistivity of the material

Factors that Affect the Resistance

There are several factors that contribute to the conductor’s resistance, including:

• The resistance depends on the dimensions of the conductor:
• Length of the conductor
• Area of the cross-section of the conductor
• The resistance of a conductor also depends on its physical state like temperature
• Resistance depends upon the material of the conductor

What is Resistivity?

The resistance we discussed previously will help us to better understand what resistivity is. Resistivity can also be called specific resistance because it represents the resistance of a material with specific dimensions. Resistivity is defined as a material’s property and is the measure of the resistance of a meter cube of a conductor.

According to the experiment, it has been discovered that the resistance of a conductor R is directly proportional to the length L of the conductor and is inversely proportional to the cross-sectional area of the conductor. Therefore, resistivity ρ can be expressed as:

R ∝ L (1)

R ∝ 1/A (2)

In the case of equations (1) and (2) combined, we obtain

R ∝ L/A

R = ρ L/A

ρ = R A/L (3)

Where,

L is the length of the conductor

A is the cross-sectional area of the conductor

R is the resistance of the material

By assuming that a conductor has a length and cross-section area of 1m and 1m2 respectively, the equation (3) is expressed as ρ = R. This means that resistivity is defined as the resistance of a wire with a length of 1m and a cross-section area of 1m2. Ohm-meter is the SI unit of resistivity, and it is directly proportional to the temperature of the material. A material’s resistivity is determined solely by its nature and physical conditions like temperature.

Difference Between Resistance and Resistivity

Knowing resistance and resistivity, we can now examine the main differences between them:

1. Resistivity is the measure of the resistance of materials with fixed dimensions, as opposed to resistance, which is the opposition to the flow of current.
2. A conductor’s resistance is equal to its cross-sectional area divided by its length, while a material’s resistivity is equal to the product of the resistance and the area divided by the length of the conductor.
3. The Resistance of the material is determined by its dimension, like length and cross-sectional area, whereas resistivity is determined by the nature and temperature of the material.
4. Resistivity is represented as ρ whereas resistance is represented by the symbol R, which is also the proportionality constant in Ohm’s law.
5. In the case of resistance, the SI unit is ohm whereas, in the case of resistivity, the SI unit is ohm-meter.

Conclusion

The concept of resistivity and resistance in the context of electricity and magnetism is critical in physics. In this article, we discussed specifically electrical resistance, which refers to the opposition to the flow of current in a conductor. In addition to an in-depth understanding of resistance and resistivity, we discussed the factors that affect both. Ultimately, we emphasized the differences between the two concepts. The article also discussed definitions, expressions, and simplified explanations of both of these physics concepts. Thus, we are able to conclude that this article clearly explained the difference between resistance and resistivity and how they are different from each other despite their similarity in names.