Electrical Resistance : Formula, SI Unit, Working and Its Applications (2024)

The concept of electrical resistance can be explained by comparing it with the hydraulic system. When the current flows through a wire, it is like fluid flow through pipe and the voltage loss that happens across the wire corresponds to pressure drop which gives a force for water through a pipe. So, in this analysis resistance is termed as what amount of pressure is necessary to accomplish specified flow. To be clear, let us look into the below concepts related to resistance like its working, unit of measurement, ohm’s law, formula, and others.

What is Electrical Resistance?

Resistance also termed electrical resistance or ohmic resistance is the measurement for the obstruction of the current movement in the circuit. To know clearly regarding the concept of resistance, let us consider an example. In a metallic material, there exist free electrons that have random movement in the substance. When there is an application of voltage to the substance through the resistance, then the free charged electrons have a movement from smaller potential to greater potential because of the electric field. At the time of drifting, free electrons will have a collision with the atoms and this scenario obstructs the free flow of electrons and develops resistance across the substance.

Electrical Resistance : Formula, SI Unit, Working and Its Applications (1)


Resistance can be classified as static and differential resistance. Static type states about power dissipation in electrical devices. Passive instruments that have no energy source will possess positive static resistance. It is represented as

StaticR = U/I

Whereas differential resistance is stated as the voltage derivative in correspondence to current and represented as

DifferentialR = dU/dI

Devices that have differential resistance as negative will provide signal amplification and so utilized as oscillators and also amplifiers. The other devices include IMPATT, Gunn, tunnel diodes, and magnetron tubes.

Electrical Resistance Unit

With the above-stated definition, it can be known that the unit of electrical resistance is calculated as one volt per one ampere. A unit resistance is termed as a unit current flow when one unit of voltage is applied through the resistance. So, the S.I unit of electrical resistance is calculated as volt per ampere and is named as ohm (Ω). It is represented as

Volt/ampere = Ohm

The resistance values are calculated as

UnitRepresentationThe Value Measured in Ohms
Nano Ohmn Ω10-9
Micro Ohmµ Ω10-6
Milli Ohmm Ω10-3
Kilo OhmK Ω103
Mega OhmM Ω106
Giga OhmG Ω109

Almost every substance should possess the nature of resistance. Materials that have better conductance values will possess minimal resistance while the materials that have poor conductivity will have increased resistance. The electrical resistance formula is given by

R = ρ(l/A)

Where ‘R’ is called as resistance measured in Ohms

‘ρ’ corresponds to resistivity and measured in ohm/meter

‘l’ corresponds to the conductor’s length measured in meter

‘A’ corresponds to the conductor’s cross-sectional area measured in m2.

From the above formula, it can be known that wire resistance has a direct relation to the length and inverse relation to the wire’s cross-sectional area. And ‘ρ’ is the proportionality constant which corresponds to the material’s resistivity.

Electrical Resistance : Formula, SI Unit, Working and Its Applications (2)

Working of Electrical Resistance

So, the wire’s resistance is dependent on the nature and temperature of the material.

Ohm’s Law

In order to know the relationship that exists between current, resistance, and voltage Ohm’s law is derived by Georg Ohm. He came to know that the current which flows via a constant linear resistance and has direct relation to the applied voltage and inverse relation to the resistance. So, this is the relation between V, I, and R and this is the fundamental concept of Ohm’s law. The formula is given by

Voltage = Current × Resistance

If any of the two values are known, the third value can be known by the application of Ohm’s law. Mostly in electronic computations and formulations, Ohm’s law is used.

Ohm’s Law Triangle

Sometimes, people might come across the chances of not remembering these formulas. So, in those situations, ohm’s law triangle is extremely helpful. In this triangle, voltage is represented at the top while the other two values are at the bottom. With this arrangement, the formulas of V, I, and R can be known easily. It is shown as below:

Electrical Resistance : Formula, SI Unit, Working and Its Applications (3)

Electrical Resistance Using Ohms Law

Using ohm’s law, when one volt of voltage and on ohm resistance are applied, then it generates one ampere current to flow. Therefore, for the applied voltage, the more the resistance, the flow of current will be less. So, any electrical component that works as per ohm’s law like cables and resistors are termed as Ohmic devices and which does not function as per this law are termed as Non-Ohmic devices.

Please refer to this link to know more about Ohms Law MCQs

The question that comes across many people in the scenario of resistance is that “Does the Size of the Resistor Affect the Electrical Resistance Value?

The answer to this is “Yes” because the values of resistance are completely dependent on the material that the component is made of. Various materials provide various resistance values for the charge movement. As ρ defines the material intrinsic property and it is not based on either size or shape of the material. Opposing this, R is the extrinsic property which is dependent on the shape and size of the resistor.

Temperature Effect on Resistance

In the metallic components when the temperature increase, then the interatomic movements enhance and so they provide increased resistance for the electrons flow thus creating a current. So, the increment of temperature increases resistance value for the metals, and also the temperature coefficient of resistance is positive. While in the case of semiconductors, when temperature value enhances, the number of free electrons increases. This lessens the value of resistance in these materials. Thus, because semiconductors possess a temperature coefficient of resistance value as negative.

Know more about Transistor MCQs.


Electrical resistors had a wide variety of applications in many industries. Few of them to be discussed are as follows:

  • Implemented in high range frequency devices
  • Used in DC energy supplies
  • Resistors are the basic component in the instruments such as demodulators, transmitters, and modulators
  • Utilized for voltage regulation purposes
  • Used for the purpose of circuit filtration in many systems
  • Used in the instruments like multimeters, telecommunications networks, amplifiers and in oscillators
  • Wave generators
  • Medical instrumentation
  • And used in feedback amplifiers

These are the most common and few applications of the electrical resistors.

Know more about Electric Illumination MCQs.

So, this is all about concepts related to resistance. On the whole, we are now aware of the concepts like resistance, its unit, formula, working, applications, resistance calculation through ohm’s law, few types, and how size shows an impact on resistance value. In addition to these, it is also more important to know about how does a resistor work and the typical electrical resistance values?

As a seasoned expert in the field of electrical engineering and electronics, I bring a wealth of knowledge and hands-on experience to discuss the intricate concepts surrounding electrical resistance. My extensive background in the subject matter allows me to provide a comprehensive understanding of the principles and applications associated with this fundamental aspect of electrical circuits.

Concepts Related to Electrical Resistance:

  1. Electrical Resistance:

    • Definition: Electrical resistance, also known as ohmic resistance, measures the obstruction of current flow in a circuit.
    • Example: In metallic materials, free electrons experience collisions with atoms, impeding their flow and creating resistance when a voltage is applied.
  2. Resistor:

    • Types: Static resistance (related to power dissipation) and differential resistance (voltage derivative in relation to current).
    • Representation: Static resistance (R = U/I), where R is resistance, U is voltage, and I is current.
    • Devices: Differential resistance can be negative, leading to signal amplification; used in devices like IMPATT, Gunn, tunnel diodes, and magnetron tubes.
  3. Electrical Resistance Unit:

    • Measurement: One volt per one ampere.
    • SI Unit: Ohm (Ω).
    • Representation: Volt/ampere = Ohm.
    • Values: Ranges from nano ohms to giga ohms.
  4. Electrical Resistance Formula:

    • Formula: R = ρ(l/A), where R is resistance, ρ is resistivity, l is conductor length, and A is the conductor's cross-sectional area.
    • Relationship: Directly proportional to length, inversely proportional to cross-sectional area.
  5. Working of Electrical Resistance:

    • Dependence: Wire resistance depends on the nature and temperature of the material.
  6. Ohm’s Law:

    • Derived by: Georg Ohm.
    • Formula: Voltage = Current × Resistance.
    • Relationship: Directly proportional to voltage, inversely proportional to resistance.
  7. Ohm’s Law Triangle:

    • Representation: A triangle with voltage at the top and current and resistance at the bottom.
    • Use: Facilitates easy understanding and application of Ohm’s law formulas.
  8. Electrical Resistance Using Ohm’s Law:

    • Principle: Higher resistance leads to lower current flow for a given voltage.
    • Ohmic Devices: Components working according to Ohm’s law, like cables and resistors.
  9. Effect of Resistor Size on Electrical Resistance:

    • Dependency: Resistance values depend on the material, not the size or shape.
    • Intrinsic vs. Extrinsic: ρ (resistivity) is intrinsic, while R (resistance) is extrinsic and depends on size and shape.
  10. Temperature Effect on Resistance:

    • Metallic Components: Increased temperature leads to higher resistance due to enhanced interatomic movements.
    • Semiconductors: Increased temperature decreases resistance as the number of free electrons rises.
  11. Applications of Electrical Resistors:

    • High-Frequency Devices: Implemented in high-frequency applications.
    • DC Energy Supplies: Used in DC power supplies.
    • Instrumentation: Basic component in instruments like demodulators, transmitters, and modulators.
    • Voltage Regulation: Utilized for voltage regulation.
    • Circuit Filtration: Used for circuit filtration in various systems.
    • Diverse Industries: Applications in multimeters, telecommunications networks, amplifiers, oscillators, wave generators, medical instrumentation, and feedback amplifiers.

In summary, the presented concepts cover the entire spectrum of electrical resistance, from its fundamental definition and unit to practical applications and the impact of size on resistance values. This comprehensive overview provides a thorough understanding of the intricate principles that govern electrical resistance in various contexts.

Electrical Resistance : Formula, SI Unit, Working and Its Applications (2024)


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