Which one of the following pairs of metals are very good conductors of heat?
Silver and Copper
Understanding Heat Conduction in Metals
Heat conduction is the transfer of thermal energy through a material or between materials that are in direct contact. This energy transfer happens due to the vibration and collision of particles (like atoms or molecules) within the material, and also through the movement of free electrons, especially in metals.
Why Metals are Excellent Heat Conductors
Metals are generally very good conductors of heat compared to non-metals or insulators. This is because metals have a structure that includes many free electrons. These free electrons can move easily throughout the metal and efficiently carry thermal energy from hotter parts to colder parts. This process is much more effective than just the vibration of atoms.
Comparing Thermal Conductivity of Common Metals
Different metals conduct heat with varying degrees of efficiency. This property is measured by their thermal conductivity. A higher thermal conductivity means the material is a better conductor of heat.
Here is a comparison of the thermal conductivity of the metals mentioned in the options, relative to each other:
| Metal | Relative Thermal Conductivity |
|---|---|
| Silver (Ag) | Highest among common metals |
| Copper (Cu) | Very High (Slightly less than Silver, but very close) |
| Gold (Au) | High (Less than Copper) |
| Aluminum (Al) | High (Less than Gold) |
| Lead (Pb) | Significantly lower than Silver/Copper |
| Mercury (Hg) | Significantly lower than Silver/Copper (and it's a liquid metal) |
Identifying the Very Good Heat Conductors
Based on thermal conductivity, Silver is the best conductor of heat among all metals at room temperature. Copper is the second best, with a conductivity value very close to that of Silver. Because of its lower cost compared to Silver and Gold, Copper is widely used in applications where good heat conduction is required, such as in cookware, heat sinks, and electrical wiring (since electrical conductivity and thermal conductivity are often related).
Let's look at the pairs given in the options:
- Silver and Copper: Both Silver and Copper are known to be very good conductors of heat. Silver is the best, and Copper is the second best.
- Silver and Lead: Silver is very good, but Lead is a relatively poor conductor compared to Silver or Copper.
- Copper and Mercury: Copper is very good, but Mercury has a significantly lower thermal conductivity, even though it's a metal (it's also a liquid at room temperature, which affects its properties).
- Lead and Mercury: Both Lead and Mercury have significantly lower thermal conductivity compared to Silver and Copper.
Therefore, the pair of metals that are very good conductors of heat is Silver and Copper.
Revision Table: Key Heat Conduction Concepts
| Concept | Description | Key Point for Metals |
|---|---|---|
| Heat Conduction | Transfer of thermal energy through direct contact. | Efficient in metals due to free electrons. |
| Thermal Conductivity | A material's ability to conduct heat. Higher value means better conductor. | Varies greatly among metals. |
| Best Conductors | Materials with highest thermal conductivity. | Silver is best, Copper is second best among common metals. |
Additional Information on Thermal Conductivity
Thermal conductivity is an important material property used in various engineering applications. Materials with high thermal conductivity are used in heat exchangers, cooling systems, and cooking utensils to efficiently transfer heat. Materials with low thermal conductivity, like plastics, wood, or foam, are used as thermal insulators to prevent heat transfer.
The Wiedemann-Franz law states that the ratio of thermal conductivity to electrical conductivity is proportional to temperature for metals. This is because both heat and electrical charge are primarily transported by the free electrons in metals. Thus, metals that are good electrical conductors are usually also good thermal conductors.
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