Lesson 13



Name:ETP Section:t3 Start Time:12:59:18 Instructor:pattersonet Course:421



1. In your own words... What is a phonon? What are some characteristics or properties of phonons?

Enter your answer here:



2. Given the expression for the Debye temperature, and the table of data below, state which solid, copper or lead, you expect to have the higher Debye temperature, and briefly explain.

Now, given the table of data, actually estimate the Debye temperature for copper and for lead. Compare your calculated values to those in the table in the text. What explanation(s) can you offer for the agreement or disagreement?

Solid Sound speed vs**
(m/s)		 Density
(kg/m3)		 Molecular weight
kg/mole
Copper 5010 8890 0.0636
Lead 1960 11,300 0.2072
**Note: sound speeds given for plane longitudinal waves. Speeds for plane transverse waves are much smaller
(on the order of 1/2 to 1/3 of the longitudinal wave speed).

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3. According to the Debye model, for nonmetallic materials,

Check the correct answer:
a) Cv goes as T3 for all T.
b) Cv is independent of T for all T.
c) Cv is independent of T at low temperatures but goes as T3 at high temperatures.
d) Cv goes as T3 at low temperatures but is independent of T at high temperatures.

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