Resistivity

What is Resistivity?

• Definition: Measure of how strongly a material opposes the flow of electric current.

• Resistance Measurement: The resistance of a one-metre cube of the material.

• Common Materials: Resistivity values differ among materials; particularly relevant for electrical conductors and insulators.

Key Facts about Resistivity

• Resistance: Typically very low for conductor materials; expressed in microhms (μΩ).

• Specific Resistance Format: Expressed as μΩm.

• Example: Resistivity of copper is 0.0172 μΩm (i.e., resistance of a one-metre cube of copper).

Resistance Representation

• Specific resistance or resistivity symbol: Greek letter rho (ρ).

• Resistance Calculation: The resistance of a conductor can be calculated using the specific resistance value.

Calculation Examples

• Resistivity Calculation Formula:

  • Formula: R = PL / a

  • where:

    • ( P (Rho) ) = resistivity of the material (S metre)

    • ( L ) = length of the conductor (metre)

    • ( A ) = cross-sectional area (m²)

    • R = Resistance

• Example Calculation:

  • For 1,000m of a 16mm² copper conductor using ( P = 17.2 x 10^-9) metre:

  • Calculation: ( R = P x L / a………. R = 17.2×10^-9 × 1000 / 16×10^-6 = ^1.07Ω