Q. Which among the following has the least thermal conductivity?

The correct answer is: d) Alloy

Explanation:

Thermal conductivity is a measure of a material’s ability to conduct heat. It varies significantly across different classes of materials due to their atomic structure, bonding, and the presence of impurities or defects. Let’s analyze each option to determine which has the least thermal conductivity.

1. Metal (Option a):

– Thermal Conductivity: Metals are generally excellent conductors of heat. This is because they have free electrons that can move easily throughout the lattice, facilitating efficient heat transfer.

– Examples:

– Copper: ~400 W/m·K

– Aluminum: ~205 W/m·K

2. Semiconductor (Option b):

– Thermal Conductivity: Semiconductors have moderate thermal conductivity, higher than insulators but lower than metals. The presence of both electrons and holes contributes to heat conduction, but their effectiveness is less than that in metals.

– Examples:

– Silicon: ~150 W/m·K

– Germanium: ~60 W/m·K

3. Superconductor (Option c):

– Thermal Conductivity: Superconductors exhibit unique thermal properties, especially below their critical temperature where they enter the superconducting state. In this state, electrical resistance drops to zero, and thermal conductivity can be affected by factors like electron pairing (Cooper pairs) and phonon scattering. Generally, their thermal conductivity is lower than that of normal metals but can vary based on the material and temperature.

4. Alloy (Option d):

– Thermal Conductivity: Alloys, which are mixtures of two or more elements (typically metals), usually have lower thermal conductivity compared to their pure metal counterparts. The presence of different atoms introduces defects and scatters phonons (heat carriers), thereby reducing the efficiency of heat transfer.

– Examples:

– Steel: ~50 W/m·K

– Brass: ~120 W/m·K

Conclusion

Among the options provided, alloys consistently exhibit lower thermal conductivity compared to pure metals, semiconductors, and even superconductors in many cases. This reduced thermal conductivity is due to the disrupted lattice structure and the presence of multiple types of atoms, which impede the free movement of heat carriers.