Which term describes the property that measures the rate at which heat passes through a material when there is a temperature difference?

• A. Volume
• B. Thermal expansion
• C. Thermo-electricity
• D. Thermal conductivity

Answer: (D)

Heat moves through a material most efficiently when there’s a temperature difference, and the property that describes how readily that heat flows is thermal conductivity. It’s the material’s measure of how easily heat can conduct through it. In Fourier’s law, heat flow per unit area is proportional to the temperature gradient and the proportionality constant is k, the thermal conductivity. So for a slab with a temperature difference ΔT across it, the steady heat transfer rate scales with k: higher k means more heat passes through per unit temperature difference, while lower k means heat passes more slowly.

Copper, with high thermal conductivity, quickly conducts heat, whereas insulators like wood or foam have low thermal conductivity and resist heat flow. The units are watts per meter kelvin (W/m·K). Other terms describe different ideas—volume relates to space, thermal expansion to size change with temperature, and thermo-electric effects to converting heat into electricity—so the term that matches the description is thermal conductivity.