Topic explanation

Standard explanation

For a uniform conductor, R=ρL/A.

Key points

• For a uniform conductor, R=ρL/A.
• Resistance is directly proportional to length and inversely proportional to cross-sectional area.
• Resistivity is a material property with SI unit Ω·m.
• Conductivity is σ=1ρ.
• For moderate temperature changes, ρT=ρ0[1+α(T−T0)].
• Metals normally have positive temperature coefficients.
• Semiconductors normally show decreasing resistance as temperature rises.
• Low-temperature-coefficient alloys are used in stable standard resistors.

Labelled diagram