310102c Characteristics of Conductors Mar 2025 (TF)

Resistance

The opposition to the flow of electric current, measured in ohms (Ω).

Conductor

A material that allows the flow of electric current, characterized by one to three electrons in the valence shell.

Insulator

A material that resists the flow of electric current, characterized by five or more electrons in the valence shell.

Semi-conductor

A material that can act as either a conductor or an insulator depending on conditions, having four electrons in the valence shell.

Length of Conductor

One of the four factors affecting resistance; longer conductors have higher resistance.

Cross-sectional area

The area of the conductor's cross-section; larger cross-sectional areas result in lower resistance.

American Wire Gauge (AWG)

A standardized wire gauge system that indicates the diameter of the wire; larger gauge numbers correspond to smaller wire diameters.

Static resistivity (ρ)

A property of a material that quantifies how much it resists current flow, measured in ohm-metres (Ω-m).

Temperature coefficient (α)

A factor that indicates how the resistance of a material changes with temperature, measured in per degree Celsius (°C change).

Formula for Resistance (R)

R = ρ(L/A) where R is resistance, ρ is static resistivity, L is length, and A is cross-sectional area.

Effect of Temperature on Resistance

Resistance can increase or decrease with temperature changes, depending on the material's temperature coefficient.

Copper resistivity at 20˚C

17.2 x 10^-9 Ω•m.

Aluminum resistivity at 20˚C

28.3 x 10^-9 Ω•m.

Resistance calculation formula

R2 = R1[1 + α(t2 - t1)] for calculating resistance at a new temperature.