What is the measure of how well a material transfers heat, which can vary with temperature?

• A. Thermal Conductivity (k)
• B. Heat Transfer Coefficient (h)
• C. Emissivity (ε)
• D. Density (ρ)

Answer: (A)

Thermal conductivity is the property that quantifies how readily heat flows through a material when there’s a temperature difference. It’s described by Fourier’s law, where the heat flux q" equals the negative product of the thermal conductivity k and the temperature gradient: q" = -k ∂T/∂x. A larger k means heat moves through the material more easily; a smaller k means it acts more like an insulator. Crucially, k can vary with temperature, so the material’s ability to transfer heat changes as temperature changes.

This is different from the heat transfer coefficient, which combines surface effects and fluid flow to describe convection at a boundary rather than conduction through the material itself. Emissivity relates to radiative heat transfer from a surface, and density is just mass per unit volume with no direct measure of heat transfer capability.