Question
Explain the variation of conductivity with temperature for:
- A metallic conductor.
- Ionic conductors.
- Semiconductors.
✓
Answer
Conductivity of a metallic conductor $\sigma=\frac{1}{\rho}=\frac{\text{ne}^2\tau}{\text{m}}.$
- With rise of temperature, the collision of electrons with fixed lattice ions/ atoms increases so that relaxation time $(\tau)$ decreases. Consequently, the conductivity of metals decreases with rise of temperature.
- Conductivity of ionic conductor increases with increase of temperature because with increase of temperature, the ionic bonds break releasing positive and negative ions which are charge carriers in ionic conductors.
- In the case of a semiconductors, when temperature increases, covalent bonds break and charge carriers (electrons and holes) become free i.e., n increases, so conductivity increases with rise of temperature.
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