Band Theory of Solids
11.2 Band Theory of Solids
Learning Objectives
- Describe two main approaches to determining the energy levels of an electron in a crystal
- Explain the presence of energy bands and gaps in the energy structure of a crystal
- Explain why some materials are good conductors and others are good insulators
- Differentiate between an insulator and a semiconductor
Band Theory
Practice!
| Practice 11.2.1 |
|---|
| An energy band in a solid consists of: |
| A. an infinite number of levels, with each level corresponding to a point in a box. |
| B. a large number of energy levels so closely spaced that they may be regarded as a continuous band. |
| C. an infinite number of wave functions, with each wave function corresponding to a point in a box. |
| D. a large number of electrons so closely spaced that they may be regarded as a continuous band of electric charge. |
| E. an infinite number of electrons, with each electron corresponding to a point in a box. |
| Practice 11.2.2 |
|---|
| If an electric field is applied to a metal: |
| A. very few electrons are excited into the conduction band. |
| B. electrons having energies near the Fermi energy require only a small amount of additional energy from the applied field to reach nearby empty energy states. |
| C. electrons having energies near the bottom of the band require only a small amount of additional energy from the applied field to reach nearby empty energy states. |
| D. the principal mode of conduction is through the motion of holes in the filled part of the band. |
| E. the Fermi energy EF becomes equal to the applied electric field E. |
| Practice 11.2.3 |
|---|
 If you push on these electrons (apply a voltage to the material), which ones will move? |
| A. All of them in bands 1,2,3 |
| B. Only the top-most one in band 3 |
| C. All of them in band 3 |
| D. Only the top few in band 3 |
| E. None of them will move |
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