Which law applies to conduction?

Which law applies to conduction?

• A. Fourier's Law
• B. Newton's Law of Cooling
• C. Stefan-Boltzmann Law
• D. Planck's Law

Answer: (A)

Conduction is heat transfer driven by a temperature difference within a material, without relying on bulk motion of the medium. The law that describes this mechanism is Fourier's law: the heat flux per unit area is proportional to the negative temperature gradient, q" = -k ∇T. The negative sign shows heat flows from hot to cold, and k is the material’s thermal conductivity, indicating how easily heat moves through the material. In a simple one-dimensional slab, this leads to Q = k A (T_hot − T_cold) / L for steady, uniform properties, or locally q" = -k dT/dx. The other laws describe different heat transfer modes. Newton’s law of cooling pertains to convection, relating the heat transfer rate to the temperature difference between a surface and its surrounding fluid via a convection coefficient h. Stefan-Boltzmann and Planck describe radiation: q" = εσ(T^4_hot − T^4_cold) for radiative exchange between surfaces, and Planck’s law gives the spectral distribution of blackbody radiation, not conduction.

Conduction is heat transfer driven by a temperature difference within a material, without relying on bulk motion of the medium. The law that describes this mechanism is Fourier's law: the heat flux per unit area is proportional to the negative temperature gradient, q" = -k ∇T. The negative sign shows heat flows from hot to cold, and k is the material’s thermal conductivity, indicating how easily heat moves through the material. In a simple one-dimensional slab, this leads to Q = k A (T_hot − T_cold) / L for steady, uniform properties, or locally q" = -k dT/dx.

The other laws describe different heat transfer modes. Newton’s law of cooling pertains to convection, relating the heat transfer rate to the temperature difference between a surface and its surrounding fluid via a convection coefficient h. Stefan-Boltzmann and Planck describe radiation: q" = εσ(T^4_hot − T^4_cold) for radiative exchange between surfaces, and Planck’s law gives the spectral distribution of blackbody radiation, not conduction.