Thermal Conductivity Compared
Silver vs copper vs wood — see speed of heat flow.
Key Notes
Thermal conductivity k measures how well a material conducts heat. Units: W/m·K.
k_metals: Cu ≈ 400, Ag ≈ 430, Al ≈ 240, Fe ≈ 80, Steel ≈ 50.
k_insulators: glass ≈ 0.8, wood ≈ 0.15, concrete ≈ 1, brick ≈ 0.7.
k_fluids: water ≈ 0.6, air ≈ 0.025.
k_air is very small — that's why fluff insulation works (trapped air pockets).
Wiedemann-Franz law: for metals, k/σ = (π²/3)(k_B/e)²·T — linear relation to electrical conductivity.
Materials with low k are used as insulators (foam, fiberglass, wood, plastic).
Materials with high k are used in heat sinks (copper, aluminum).
Formulas
Fourier's law (rate)
Direct dependence on k.
Wiedemann-Franz law
Universal Lorenz number for metals.
Thermal resistance
Low k ⇒ high R ⇒ good insulator.
Important Points
k of metals is 100-1000× larger than of insulators.
Air is a poor conductor (k ≈ 0.025 W/m·K). Trapped air = good insulator (foam, double-paned windows).
Diamond has the highest k of any natural material (~2200 W/m·K) — covalent lattice with high phonon transport.
Vacuum has ZERO conduction (no medium).
Why a metal feels cold to touch: high k pulls heat from your skin quickly. Wood feels warm: low k.
Wiedemann-Franz: same electrons carry both heat and current ⇒ linear k-σ relation in metals.
Thermal Conductivity Compared notes from sciphylab (also known as SciPhy, SciPhy Lab, SciPhy Labs, Physics Lab). Class 11 physics revision for JEE Mains, JEE Advanced, NEET UG, AP Physics 1/2/C, SAT, and CUET-UG.