Conduction is the transfer of heat energy through a material without the material itself moving. Think of it like a line of people passing a hot cup of tea down a row of friends – the cup (heat) moves, but the friends (material) stay in place.
In metallic solids, some electrons are not bound to any particular atom. They roam freely through the lattice of metal ions, forming a “sea” of electrons. When one part of the metal is heated, these free electrons gain energy and start moving faster, carrying heat to cooler regions.
When a free electron collides with a metal ion, it transfers some of its kinetic energy. This energy is then passed on to the next electron in line. The process repeats, creating a chain reaction that moves heat from hot to cold.
Mathematically, the heat current density \$J_q\$ is proportional to the temperature gradient:
\$ J_q = -k \nabla T \$
where \$k\$ is the thermal conductivity of the metal.
| Material Type | Free Electrons | Conductivity |
|---|---|---|
| Metal | Many | High |
| Insulator | Few | Low |
| Semiconductor | Moderate (can be increased by doping) | Variable |
Exam Tip: When answering questions about conduction, always mention the role of free electrons and how they transfer energy through collisions. Use the analogy of a “crowd” of electrons moving through the metal lattice.
Key Formula: Thermal conductivity \$k\$ is a property of the material and can be found in tables. Remember that higher \$k\$ means better conduction.
Fun Fact: ⚡️ Copper is the best conductor of electricity, but aluminium is often used in power cables because it’s lighter and cheaper, even though its conductivity is slightly lower.
When you touch a metal spoon that’s been in a hot pot, the heat travels along the spoon via free electrons, warming your hand. That’s conduction in action!