IGCSE Physics - 2.3.1 Conduction

Objective: Describe, in terms of particles, why thermal conduction is bad in gases and most liquids

Thermal conduction is the transfer of heat through a substance due to the movement of particles. In solids, particles are closely packed, allowing for efficient transfer of kinetic energy. However, in gases and most liquids, the particles are much further apart, resulting in poor thermal conduction.

Conduction in Solids

In a solid, the particles (atoms or ions) are tightly packed together in a fixed arrangement. When one end of the solid is heated, the particles at that end gain kinetic energy and vibrate more vigorously. These vibrations are readily transmitted to neighboring particles through collisions, allowing the heat energy to spread throughout the solid.

Conduction in Gases

In a gas, the particles (atoms or molecules) are widely separated and move randomly. When one end of the gas is heated, the particles at that end gain kinetic energy and move faster. However, because the particles are far apart, the energy transfer relies on collisions between particles. These collisions are infrequent and less effective at transferring kinetic energy compared to the close-packed particles in a solid.

The poor conduction in gases is due to the low density of particles and the large distances between them. The kinetic energy gained by a few particles at the hot end is not efficiently passed on to the rest of the gas.

Conduction in Liquids

In a liquid, the particles are closer together than in a gas but not as close as in a solid. They have some degree of freedom to move around, but they are still relatively close. While there is some degree of particle proximity, the movement is not as restricted as in a solid. This results in thermal conduction being less efficient than in solids, but better than in gases.

The limited conduction in liquids is because the particles are not as closely packed as in solids, leading to fewer and less effective collisions for energy transfer.

Summary Table

State of Matter	Particle Spacing	Thermal Conduction Efficiency	Reasoning
Solid	Very close	High	Efficient transfer of kinetic energy via vibrations and collisions.
Liquid	Medium	Moderate	Particles are closer than in a gas, but still have some freedom of movement.
Gas	Very far apart	Low	Infrequent and less effective collisions for energy transfer.