Resistance, resistivity and conductor geometry
Resistance belongs to a device geometry; resistivity is a material response.
Key knowledge
For a local linear isotropic conductor, J=σE and resistivity ρ_e=1/σ. A uniform straight conductor with length L, area A and uniform resistivity has resistance R=ρ_eL/A. Temperature, composition and microstructure can change resistivity; a device’s resistance also depends on its geometry.
Values and equations
J=σE; ρ_e=1/σ; R=ρ_eL/A
- J
- Current-density vector A m⁻²
- E
- Electric-field vector V m⁻¹
- σ
- Conductivity S m⁻¹
- ρ_e
- Electrical resistivity Ω m
- R
- Conductor resistance Ω
- L
- Length m
- A
- Cross-sectional area m²
Conditions and scope
- σ>0; uniform steady-current model with negligible contact/spreading resistance and constant cross-section.
- Linear isotropic response must hold over the stated field/temperature range. Non-ohmic devices, anisotropy, heating and high-frequency skin effects need a more detailed response.
Sources · 1
References
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Evidence and review
Read §9.3 local conductivity/resistivity9.6 and conductor geometry derivation9.7. Material response and device resistance are kept distinct; no universal resistivity or room-temperature coefficient is imported.
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Entry details
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- foundation-physics-resistivity-geometry
- Revision
- foundations-refresh.1
- Structured reference record
- Foundational reference additions