t3s201s03 - EMSE 201 Introduction to Materials Science...

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EMSE 201 — Introduction to Materials Science & Engineering 23 April 2003 Name: SOLUTION Department of Materials Science and Engineering 1 of 6 Case Western Reserve University Test #3 — 50 minutes; 150 points; 7 questions; 6 pages; 15% of course grade No calculators or formula sheets are allowed. Where numerical answers are requested, full credit will be given for correctly setting up the calculation and for specifying the correct units . 1) (21 points) Multiple choice. For each question, circle all of the given options that apply (0.5 points per correctly circled or uncircled option, except question j which is 1 point each) : a) Which of the following categories of materials has the highest concentration of charge carriers? metals semiconductors ceramics polymers b) Which of the following categories of materials has the highest mobility of charge carriers? metals semiconductors ceramics polymers c) Which of the following categories of materials is most likely to contain ionic conductors? metals semiconductors ceramics polymers d) Which of the following categories of materials has linearly increasing electrical resistivity with increasing temperature? metals semiconductors ceramics polymers e) For which of the following categories of materials is the concentration of charge carriers proportional to a Boltzmann factor? metals intrinsic semiconductors extrinsic semiconductors insulators f) For which of the following elemental solids does metallic electrical conductivity arise from a partially filled valence band? Mg Na Cu C (diamond) g) For which of the following elemental solids does metallic electrical conductivity arise from overlap of an empty band with a filled band? Mg Ge Cu Zn h) Which of the following elemental solids has a band gap with energy greater than 2 eV? Mg Ge Si C (diamond) i) Which of the following elemental solids has a band gap with energy less than 2 eV? Mg Ge Si Cu j) Which value of the Pilling-Bedworth ratio is expected to correspond to a protective oxide coating?
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EMSE 201 — Introduction to Materials Science & Engineering 23 April 2003 Department of Materials Science and Engineering 2 of 6 Case Western Reserve University 0.5 1.5 3.5 2) The electrical conductivity of a specimen of silicon at room temperature is 10 3 –1 m –1 . The hole concentration is known to be 1.0 × 10 23 m –3 . a) (6 points) Is the specimen intrinsic , n-type extrinsic , or p-type extrinsic? Explain. The given hole concentration (1.0 × 10 23 m –3 ) is several orders of magnitude higher than the hole concentration in intrinsic silicon at room temperature (~10 17 m –3 from the graph at left) (3 points). Therefore one can conclude that the material is p-type extrinsic (3 points). b)
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t3s201s03 - EMSE 201 Introduction to Materials Science...

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