Conduction
Conduction is the process of heat transfer through a material from a region of higher temperature to a region of lower temperature, without any overall movement of the substance.
Conduction in Metals
- Metals contain free (mobile) electrons that move through the metal lattice.
- When heated at one end, these electrons gain kinetic energy and move faster.
- They collide with other electrons and positive ions in cooler regions, transferring energy.
- Additionally, metal ions vibrate more vigorously and pass on their vibrations to neighbouring ions.
- Thus, heat is transferred efficiently from the hot end to the cold end through both free electrons and ion vibrations.
Conduction in Non-Metallic Solids
- Non-metals do not have free electrons.
- Heat is transferred only by vibration of atoms within the lattice.
- This process is much slower and less efficient than in metals.
- Hence, non-metals are poor conductors (thermal insulators).
Facts about Conduction
- Conduction cannot occur in a vacuum.
- Metals conduct heat better than non-metals.
- Conduction can occur in solids, liquids, and gases — but least efficiently in gases.
Why Gases Conduct Heat Poorly
Gases have very few molecules, spaced far apart. Energy transfer occurs only by collisions and diffusion during random molecular motion. Hence, conduction in gases is very weak.
Experimental Demonstration — Comparing Conductivity
Equal heat is applied to several metal rods with wax rings fixed along their length. The rod that loses the wax rings fastest is the best conductor of heat.
Observation
The metal that conducts heat fastest will have fewest wax rings left after a fixed time. This experiment demonstrates comparative thermal conductivity.
Comparison: Good Conductors vs Insulators
| Property | Good Conductors (e.g. Metals) | Insulators (e.g. Wood, Plastic) |
|---|---|---|
| Free Electrons | Present and mobile | Absent |
| Heat Transfer Mechanism | By free electrons and ion vibrations | By vibration of atoms only |
| Speed of Heat Transfer | Fast | Slow |
| Thermal Conductivity | High | Low |
| Examples | Copper, Aluminium, Silver | Wood, Glass, Air |
Key Idea
In solids, heat transfer by conduction is due to two processes:
• Electron movement (dominant in metals)
• Atomic vibration (dominant in non-metals)
Exam Tip
Conduction cannot occur in a vacuum — there are no particles to transfer energy. Remember: Metals → good conductors, Non-metals → poor conductors.
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