Q73
General SciencePhysics
In terms of thermal conductivity ($k$) and electrical conductivity ($\delta$), diamond has
- a.low $k$ and high $\delta$
- b.high $k$ and low $\delta$
- c.high $k$ and high $\delta$
- d.low $k$ and low $\delta$
Answer: (B) high $k$ and low $\delta$
Diamond has the highest thermal conductivity of any natural material (about $2000\,W\,m^{-1}K^{-1}$, roughly five times that of copper), because heat is carried very efficiently by lattice vibrations (phonons) through its rigid network of strong C-C bonds. But every carbon atom uses all four valence electrons in $sp^3$ covalent bonds, leaving no free electrons, so diamond is an electrical insulator: high $k$, low $\delta$. Graphite ($sp^2$, with delocalised electrons) conducts electricity; metals such as copper and silver are high in both.