1. Why is the free-electron model not applicable to semiconductors and insulators?
2. How does a semimetal differ from a normal conductor?
3. Compare the resistivities of conductors, semiconductors, and insulators at room temperature.
4. Why does the addition of impurities to a conductor increase its resistivity, whereas the addition of impurities to a semiconductor generally decreases its resistivity?
5. Would you expect carbon resistors to be useful as thermometers at room temperature and above? Explain.
6. Why are semiconductors referred to as non-ohmic?
7. Use the size of the energy gap to decide whether the following should tend to be transparent to visible light: conductors, semiconductors, and insulators.
8. Repeat Question 7 considering near-infrared light with A = 1 µm.