Resistivity, denoted by \( \rho \), is a property of a material that describes how strongly it resists the flow of electric current. It is defined by the equation:

\[ \rho = R \cdot \frac{A}{L} \]

• \( \rho \): Resistivity (Ω·m)
• \( R \): Resistance of the conductor (Ω)
• \( A \): Cross-sectional area of the conductor (m²)
• \( L \): Length of the conductor (m)

Resistivity is a material-specific constant — it does not depend on the size or shape of the material, but rather its nature and temperature.

Factors Affecting Resistivity

• Material Type: Conductors (like copper and silver) have low resistivity; insulators (like rubber or glass) have high resistivity.
• Temperature: For most conductors, resistivity increases with temperature. In contrast, some semiconductors and insulators show decreased resistivity with rising temperature.
• Impurities: Adding impurities (as in alloys) generally increases resistivity by scattering electrons more.
• Crystal Structure and Defects: Imperfections or dislocations in the atomic lattice can also affect how easily electrons flow through the material.

Resistivity plays a critical role in designing electrical components, especially when selecting materials for wires, resistors, and electronic devices.

Written by Thenura Wickramaratna