What is the main form of thermal energy transfer in solids?

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

Answer: (D)

Conduction is the main form of thermal energy transfer in solids. It happens through direct contact, as hotter particles transfer energy to neighboring cooler ones through collisions and interactions. In metals, free electrons move quickly and carry energy rapidly from the hot region to the cool region, colliding with atoms along the way. In nonmetal solids, energy primarily travels via lattice vibrations, or phonons, as vibrating atoms pass vibrational energy to their neighbors. Conduction relies on the solid’s tightly packed structure, so no bulk fluid motion is needed, which is why convection (which requires a moving fluid) isn’t the primary mechanism here. Radiation can transfer heat without contact, but in most solid materials at ordinary temperatures, it isn’t the dominant mode of heat transfer. Diffusion of heat is typically slower and not the main description for how heat moves through solids.