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Unit of resistance

Unit of resistance

Resistance is one of the most important concepts in current electricity. Students come across this real-world concept of resistance when studying electric currents. Electrical current consists of two elements, conductance and resistance.

In physics, we consider a substance to be resistive if it interferes with the flow of electric current. It is dependent upon various factors. It is related to the current and the potential difference applied. Its dimensions are length squared mass per time cubed electric current squared, and the letter R is the symbol for resistance.

Physically, resistance is the ability of a material to resist the flow of electricity. The resistance of a material depends on its physical dimensions, composition, and its temperature. In terms of fundamental properties, resistivity or specific resistance refers to how resistant a material is. For example, a conductor's resistance is extremely low, whereas the resistance of an insulator is extremely high. Conducting wires have resistance proportional to their length and inversely proportional to their cross-sectional area. Resistance is expressed as a scalar quantity using a number and appropriate units. Using the SI system, the measurement unit of resistance is Ohms.

Definition of resistance: Ohm's Law

Ohm's law states that if a conductor maintains a constant temperature with its other physical quantities, then the current in that conductor will always be proportional to the potential difference applied to its ends. If a conductor has a potential difference V between its ends, then mathematically, the current I flowing through the conductor is,
The proportionality constant is R,

Depending on the physical state and composition of the constituent material, R is the resistance of the conductor.

Dimension and Unit of Resistance Formula

Originally named for Georg Ohm, the Ohm(Ω) unit of resistance is the SI unit of resistance. The value of the quantity is 1 Ohm when 1 A of current flows through both ends of the conductor, provided the conductor has a potential difference of 1V between the two ends.

1Ω =1V/1A
The dimension of resistance is
[M] [L2] [T-3] [I-2]

SI Unit of Resistance

The unit of resistance is ohms, which is equal to one volt per amp. In some cases, the Greek letter omega represents the unit. The formula for Ohm is as follows;
R= V/I
The unit ohm-meter or ohm-m can measure specific resistance or resistivity.

International Definition for the Unit Ohm

The resistance of a mercury column consisting of 106.3 cm in length, 14.4521 g in mass, and melting ice temperature is 1 Ohm.

Electrical Conductance

The reciprocal of resistance is the electrical conductance. Therefore, a material's conductivity determines how easily the current passes through. The SI unit of electrical conductance is the siemens (S) or mho, opposite of the SI unit of electrical resistance, the ohm.

Specific Resistance

Conductors have a resistance R that depends on their length L, cross-section A, and composition. When a conductor has a fixed cross-section, its resistance is proportional to its length. When the length is constant, the resistance is inversely proportional to the cross-section. These two relationships in combination give the following:
R ∝L/A
The specific resistance is a proportionality constant here.

The resistivity or specific resistance of a material is the resistance of a homogeneous segment (part) of that material having a unit length and unit cross-section. Mathematically it is represented as:
ρ= RA/L

Some Useful Units are Listed Below


Conversion to Ohm

emu resistance

10-9 𝛀

Kilo ohm (k 𝛀)

103  𝛀

Mega ohm (M 𝛀)

106 𝛀

Stat ohm (stat 𝛀 )

9 X 1011 𝛀

Did you know?

  • There are special materials that exhibit a superconducting phase. During the superconducting phase (at very low temperatures), superconductors have zero resistance.
  • The resistance varies with temperature. In metals, resistance increases as temperature increases if other physical quantities are constant. Glass, however, exhibits a significant decrease in resistivity at high temperatures.
  • Semiconductors behave differently from metals which make them useful in electronics. For example, as semiconductors' temperature increases, their resistivity decreases.

Frequently Asked Questions about the Unit of Resistance

Ques: What is the difference between resistance and resistivity?
Resistance is the ratio of voltage (potential difference) across the ends of the conductor and the current passing through the conductor.
On the other hand, resistivity is the resistance of a material having a unit area of cross-section and unit length.

Ques: How does temperature affect the resistance in a conductor?
The temperature affects the resistance of the conductor proportionally. When the temperature of a conductor increases, the particle vibration increases and as a result, the resistance increases.

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