In solids, heat transfer due to temperature differences is primarily by which mechanism?

• A. Convection
• B. Conduction
• C. Radiation
• D. Evaporation

Answer: (B)

Conduction is the primary mechanism by which heat moves through solids when there is a temperature difference. In a solid, particles are tightly packed, so energy transfer happens through interactions between neighboring atoms and through mobile electrons rather than bulk fluid flow. Hot regions have higher energy particles that collide with neighbors, passing kinetic energy along the material. In metals, free electrons play a big role, speeding up heat transfer as they move rapidly and transfer energy to lattice ions. The speed of this transfer depends on the material’s thermal conductivity: metals with high conductivity transfer heat quickly, while insulators with low conductivity do so slowly. This idea is captured by Fourier’s law, which states that heat flux is proportional to the negative temperature gradient and the material’s conductivity. Convection involves moving fluids and isn’t the main process inside a solid, radiation is energy transfer by electromagnetic waves and can be significant in other contexts, but within a solid the dominant mechanism due to a temperature difference is conduction. Evaporation is a phase-change process from liquid to vapor and isn’t a typical mechanism for heat transfer in solids.