Dissemination of IT for the Promotion of Materials Science (DoITPoMS)

DoITPoMS Teaching & Learning Packages Introduction to thermal and electrical conductivity Questions
Introduction to thermal and electrical conductivity AimsBefore you startIntroductionIntroduction to conductionMetals: the Drude model of electrical conductionFactors affecting electrical conductionThermal conduction metalsElectrical conduction: non metalsNon-metals: thermal phononsApplicationsSummaryQuestionsGoing further
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Questions

Quick questions

You should be able to answer these questions without too much difficulty after studying this TLP. If not, then you should go through it again!

  1. For phonons, the normal modes

    a Gain particle like behaviour under quantum mechanics.
    b Gain wave like behaviour under quantum mechanics.
    c Adopt both particle and wave like behaviour under quantum mechanics.

  2. Using the assumptions in the Free electron model, how do crystal lattices affect electrons?

    a The lattice is not taken into account, lattice imperfections and defects are ignored.
    b The lattice is not taken into account, but lattice imperfections and defects may scatter electrons.
    c The lattice and any defects are taken into account and are able to scatter electrons.

  3. Umklapp scattering is:

    a when two phonons scatter and create a third phonon with a momentum k-vector inside the first Brillouin zone and the total phonon momentum remains the same.
    b when two phonons scatter and create a third phonon with a momentum k-vector inside the first Brillouin zone and the total phonon momentum changes.
    c when two phonons scatter and create a third phonon with a momentum k-vector outside the first Brillouin zone and the total phonon momentum changes.

  4. According to the Wiedemann-Franz law, which of the following is true?

    a thermal conductivity is inversely proportional to electrical conductivity in all materials.
    b thermal conductivity is proportional to electrical conductivity in all materials.
    c thermal conductivity is inversely proportional to electrical conductivity in metals.
    d thermal conductivity is proportional to electrical conductivity in metals.

  5. Which of the following statements about electrical conduction in nearly pure materials are true?

    a At low temperatures, resistivity decreases to zero as the lattice no longer interferes with electron motion.
    b At low temperatures, conductivity decreases to a minimum based on residual lattice defects.
    c Dislocations and grain boundaries provide a low resistance route for electrons to travel through a material.
    d At higher temperatures, the scattering effect of thermal phonons swamps that of residual lattice defects.
    e At low temperatures, conductivity increases with the addition of high valency atoms to the bulk lattice, as they provide more electrons to the lattice.
    f At low temperatures conductivity does not increase beyond a maximum due to imperfections in at the lattice scattering electrons.

  6. Which of these is the correct order in terms of best to worst electrical conductivity (assumed pure materials) ?

    a Nb3Sn at 4K, Ag at 300K, Au at 300K, Nb3Sn at 300K, Cu at 300K.
    b Ag at 300K, Cu at 300K, Nb3Sn at 4K , Au at 300K, Nb3Sn at 300K.
    c Nb3Sn at 4K, Ag at 300K, Cu at 300K , Au at 300K, Nb3Sn at 300K.
    d Nb3Sn at 300K, Cu at 300K, Ag at 300K, Au at 300K, Nb3Sn at 4K.
    e Nb3Sn at 4K, Cu at 300K, Nb3Sn at 300K, Ag at 300K, Au at 300K.

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