How does conduction transfer heat?

• A. By bulk fluid motion
• B. By evaporation
• C. By collisions between particles transferring energy with no net mass transfer
• D. By radiation only

Answer: (C)

Heat conduction moves energy through direct interactions between particles, transferring kinetic energy when they collide or vibrate, without the material as a whole moving. In metals, free electrons rapidly carry energy from hotter to cooler regions and then transfer it to the surrounding atoms; in other materials, lattice vibrations (phonons) pass energy along as particles collide. Conduction can occur in solids, liquids, and gases, but it happens without any bulk flow of the substance—contrast that with convection, which relies on overall fluid movement. Evaporation involves a phase change, not just energy transfer by particle interactions, and radiation transfers energy through electromagnetic waves, not by particle collisions. The described mechanism—energy transfer through collisions between particles with no net mass transfer—best captures conduction.