Conduction of Heat

What is Conduction?

Conduction is the process of heat transfer through a solid material without the overall movement of the material itself. It happens when particles in a solid vibrate and pass their energy to neighbouring particles through collisions.

In conduction, heat moves from the hotter part of the solid to the cooler part by the transfer of kinetic energy between particles. Unlike convection or radiation, conduction requires a medium and mainly occurs in solids because their particles are closely packed.

How Conduction Works

Particles in a solid are arranged in a fixed, closely packed structure. When one part of the solid is heated, its particles vibrate more vigorously. These vibrations cause the particles to collide with neighbouring particles, transferring energy from the hotter region to the cooler region.

In metals, conduction is much faster because metals contain free electrons. These free electrons move quickly through the metal, carrying energy and transferring it rapidly between particles. This is why metals are good conductors of heat.

Non-metals, such as wood or plastic, do not have free electrons. Heat transfer in non-metals happens mainly through vibrations of atoms and molecules, which is slower than conduction in metals.

For instance, when you touch a metal spoon that has been sitting in a hot cup of tea, the handle quickly becomes hot because the free electrons transfer heat rapidly along the spoon.

Factors Affecting Conduction

Several factors affect how quickly heat is conducted through a material:

• Material type: Metals conduct heat well due to free electrons, while non-metals conduct heat poorly.
• Thickness of the material: Thicker materials increase the distance heat must travel, increasing resistance to heat flow and thus slowing conduction.
• Temperature difference: The greater the temperature difference between the two ends of the material, the faster the rate of heat conduction.

For example, a thin metal pan will conduct heat from the stove to the food faster than a thick wooden spoon.

Example: Calculating Heat Transfer Rate

Imagine a metal rod 0.5 m thick with one end at 1006C and the other at 206C. The temperature difference is $100 - 20 = 80^\circ C$. If the rod is made of copper (a good conductor), heat will transfer faster than if it were made of wood.

The rate of heat transfer by conduction can be calculated using the formula: $Q = \frac{kA\Delta T}{d}$, where $Q$ is the heat transfer rate, $k$ is the thermal conductivity of the material, $A$ is the cross-sectional area, $\Delta T$ is the temperature difference, and $d$ is the thickness of the material.

Example: Comparing Metals and Non-Metals

Metals conduct heat faster than non-metals because of free electrons. For example, copper conducts heat about 100 times faster than wood.

Example: Effect of Thickness on Conduction

If you double the thickness of a material, the heat takes longer to pass through because the energy must travel further.