Which statement describes conduction energy transfer?

• A. By bulk fluid motion
• B. By photon emission
• C. By phase change
• D. By collisions between particles transferring energy with no net mass transfer

Answer: (D)

Conduction is energy transfer through microscopic interactions between neighboring particles, with no overall movement of the substance. When one region is hotter, its particles have more energy and pass some of that energy to nearby particles by collisions and lattice vibrations. In solids, especially metals, free electrons also help spread energy quickly through collisions. This explains why a hot object can warm another object it’s touching without the matter itself bulk-moving. Convection, by contrast, involves bulk fluid motion carrying energy, and radiation transfers energy by photons through space. Phase changes involve latent heat during melting or vaporization, which is a different mechanism. So conduction is best described as energy transferred by collisions between particles with no net mass transfer.