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Understanding Electrical Resistivity

Published in Electrical Properties 2 mins read

What is the SI unit for resistivity?

The SI unit for resistivity is the ohm-metre (Ω⋅m).


Electrical resistivity, often denoted by the Greek letter ρ (rho), is a fundamental property of a material that quantifies how strongly it resists electrical current. A low resistivity indicates a material that readily allows electric current to flow, making it a good conductor, while high resistivity signifies a poor conductor, or a good insulator.

The SI Unit: Ohm-Metre (Ω⋅m)

As per the International System of Units (SI), the standard unit for electrical resistivity is the ohm-metre. This unit is represented by the symbol Ω⋅m, combining the ohm (Ω) for electrical resistance and the metre (m) for length.

Practical Example of Ohm-Metre

To better grasp the meaning of ohm-metre, consider this practical scenario:

  • Imagine a solid cube of a material measuring 1 cubic metre (1 m³).
  • If you apply sheet contacts to two opposite faces of this cube, and the electrical resistance measured between these contacts is 1 ohm (1 Ω), then:
  • The resistivity of that material is precisely 1 ohm-metre (1 Ω⋅m).

This example from Electrical resistivity and conductivity - Wikipedia illustrates how the unit connects resistance with the material's geometry (length and cross-sectional area).

Key Information at a Glance

For quick reference, here's a summary of the SI unit for resistivity:

Quantity SI Unit Symbol
Electrical Resistivity Ohm-metre Ω⋅m

Knowing the resistivity of a material is crucial in various applications, from designing electrical circuits and components to understanding the behavior of semiconductors and insulators.