Free electrons drive heat conduction in metals

Steps:

• Recall that thermal conduction involves transferring kinetic energy through a material without net movement of matter.
• Compare materials: metals like copper have free electrons, while insulators like glass rely on lattice vibrations (phonons).
• Identify the mechanism: in metals, free electrons move quickly, carrying heat efficiently; in glass, vibrations are slower and less effective.
• Evaluate options: select the one describing free electron contribution.

Why D is correct:

• Free electrons in copper, as per kinetic theory of metals, rapidly diffuse thermal energy by colliding and transferring kinetic energy, far more efficiently than phonon conduction in glass.

Why the others are wrong:

• A: Atomic vibrations in copper are actually fast due to electrons, not slow.
• B: Atoms in solids don't move through the lattice; only electrons do in metals.
• C: Density changes relate to convection or expansion, not conduction mechanism.

Final answer: D