1. [8 pts] Multiple Choices. List the mechanisms through which thermal energy is

Question

1. [8 pts] Multiple Choices. List the mechanisms through which thermal energy is transferred in a material . Which one is the primary mechanism for thermal Which one is the primary mechanism for conduction in a metal? thermal conduction in a ceramic? A. Transfer of free electrons B. Lattice vibrations (or transfer of phonons) D Diffuion of vacancies C. Motion of dislocations 2. [6 pts] True or False. (a) The electrical conductivity of a metal (e.g., Al) increases as temperature increases. (b) In intrinsic semiconductors, the number of free electrons equals to the number of holes (n (c) As temperature increases, the electrical conductivity of Si increases. 3. [8 pts] Explain why doping in a semi-conductor could improve its electrical conductivity Hint: think about the band gap and the difference between intrinsic and extrinsic (n-type or p- type) semiconductors

Explanation / Answer

1. Three mechanism through which thermal energy can be transferred in material :

a. Conduction

b. Convection

c. Radiation

Transfer of free electrons is the primary mechanism for transfer of thermal energy.

Lattice vibration is the primary mechanism for thermal conductance in ceramic.

2.a false

2.b true

2 c true

3.Doping is nothing but adding n or p type Impurities to a semiconductor. So these impurities will contain some electrons or holes based on their impurities. When this kind of doping takes place in semiconductor and voltage is applied, these electrons will conduct electricity. In case of holes electrons due to potential excitation jumps from their original position to these holes and form immobile ions at that point whereas equal amount of holes are created from where these electrons jumped. Thus conductivity increases due to doping.

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