Question

The ratio of thermal and electrical conductivities is a function of only:

• A. Mean free path
• B. Density
• C. Temperature
• D. Fermi energy

Hint:

Wiedemann-Franz law says \(\frac{K}{\sigma}\) is proportional to temperature.

Answer 1

The Correct Option is C

Concept:
According to Wiedemann-Franz law, the ratio of thermal conductivity to electrical conductivity is proportional to absolute temperature. \[ \frac{K}{\sigma}=LT \] where, \[ K=\text{thermal conductivity} \] \[ \sigma=\text{electrical conductivity} \] \[ L=\text{Lorenz number} \] \[ T=\text{absolute temperature} \]

Step 1: Write the law. \[ \frac{K}{\sigma}=LT \]

Step 2: Identify the variable.
Since \(L\) is constant for a metal approximately, the ratio depends only on: \[ T \]

Step 3: Final answer. \[ \therefore \text{Correct Answer is (C)} \]