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ss_quiz_1 - E—344 Spring 2006 Name; \,\%’;_;§j;p. Quiz...

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Unformatted text preview: E—344 Spring 2006 Name; \,\%’;_;§j;p. Quiz 1 23 February, 2006 |D#: Honor Pledge: Use the backs of the pages if you need more space. Clearly label any work there with an appropriate question number. 1. lnSb (Indium Antimonide) is a so-called narrow bandgap semiconductor. Its gap energy is 0.17 eV. It is often used as part of a detector for infrared light in night-vision systems, for example. A) (5 pts) sketch a well—labeled energy-band diagram characteristic of lnSb. r.._.—_..____.__.t_____.... E20 PM.” _ . m. ._.w-ui.~wW—'“—' ENSW Cause-ham r2. _. #WM 5 1‘ -. ’— _ 1/4 , ‘5' . ' . _. . m .1 A V,_.:'. .... m,,.._...,.‘i...t .. ' r 3? Mints WW Mfr? haw-w PK 5 B) (10 pts) Calculate the maximum wavelength of light that could be absorbed by a 7’ crystal of pure InSb. ~.-—..... ’ V..- .‘ a.‘ _ \ i .. r , . \ rm rs... V. ‘ x‘ . \\. l————-———___ 2) (10 pts) Magnesium (Mg) has an atomic number of 12. Write its electron @ configuration using the spdf notation. Its eiectronegativity is 1.2. In contrast, sodium (Na) has an atomic number of 11 and an electronegativity of 0.9. Briefly expiain why the electronegativity of Mg is greater than that of sodium. \CD? 2-52 2%: MK N8 is V-wkm ls éfl‘ifiaTM mNdL‘ZKS ( bar we) @3ka Side of— MA Two Ks was F\\\'€c}\. M\ 1M; 1%, ‘ m \CisAS‘ OMWwa>b\ $92ch “‘3 Pa 09. W 9. I_____._____._ 3) @ (a) (5 pts) Sketch a real-space picture ofa magnesium atom using a planetary model. (b) (5 pts) The binding energies (in eV) required to remove an electron from the various electron states in magnesium are listed in the table below. Use these to sketch a qualitative energy~level diagram describing the electron energy states for a single magnesium atom. ‘ K ls 1303 L | 28 88.6 L H 2p1/2 496 L Ill 2p3/2 49.2 Pace — 7. 4. One crystallographic form of iron (Fe), the major element in steel, is body- centered cubic (BCC). In the 800 the edges of the unit cell all have the same length (a. the lattice parameter), and there are atoms located at each corner of the unit cell as well as at the body-centered position. in the form of steel referred to as martensite, the BCC Fe structure is slightly distorted into body-centered tetragonal (BCT). In this BCT structure, two of the unit cell edges have the same length (a‘) but the third (0) is slightly elongated. In BCT. the body- diagonal direction remains a close-packed direction just as it is in 800. A) (10 pts) For a so—called 1080 plain-carbon steel (Fe-0.8 wto/ocarbon), a' = 0.284 nm and c = 0.294 nm. Determine the radius of an iron atom. Show your work. B) (10 pts) The atomic packing fraction characteristic of the BCC structure is 0.68. Quantitatively compare the atomic packing fraction for this BCT form of iron to the original 800 form. ml\ J- \ \6 2 \ . "l ~1- \s 3 \7/U\ (xi-«s. J If_________ 5. The temperature dependence of viscosity is given in the graph below for five different silica-based glasses. A) (10 pts) For the glass marked (b), develop a quantitative expression for the viscosity as a function of temperature, n(T). Use this to calculate the viscosity at T=600 °C. variety of additives such a 5 sodium, boron, and aluminum. Which curve corresponds to fused silica? Briefly but specificallyjustify your answer. ® Cums. (a (@W'T.}Z§3§f’w vs W fink; “é-J \. \ CA . Rb? mvfit S k/UVL K kadfit ‘3 CD \1 \(b7 cadzkfvf . : B) (5 pts) One ofthe five glasses corresponds to fused silica while the rest contain a v Q)\ ’1': “LL; ":57 L0 ’6 ix, 113—“ kD \CQ) \ ‘ Rm- \ 2&2 ~ s A. J a L\. \ x. - AZ \ _ ....—-.—--'— _ g .. K _. \ i“ i; L: 3 ._. ‘4 ‘k \‘D J did/Q \ L) fi_________ In the following multiple-choice problems, circle the one answer which BEST completes the sentence. 3 points per problem. No partial credit. 6. Secondary bonds: a. involve dipoles; b. do not involve charge transfer; 0. are about 100 times weaker than primary bonds; ® all of the above. there is a minimum in the curve representing energy as a function of atomic separation; c. all atoms are like impenetrable (hard) spheres which can’t get any closer to each other once they touch; d. none of the above. 7. There is an equilibrium bond length between two atoms at 0 Kelvin, because: a. at such low temperatures, atoms are frozen together; @ valence electron energy levels split to satisfy the Pauli exclusion principle; 0. empty electron orbitals overlap with filled orbitals; d. none of the above. 8. Energy bands form in a polyatomic solid, because: @ a. some materials are metals and others are insulators; 10. A vacancy: a. is a point defect b. corresponds to an atom missing from a crystal lattice site c. occurs when an electron is removed from the valence band ofa material aandb 11. Most metals have a high electrical conductivity, because: a) metal atoms are small and can move quickly in a solid; electrons in metals are tightly bound to the atomic nuclei; b the valence band is partially filled or overlaps with a conduction band; the valence band is filled; - e) none of the above. |____________ 12. A crystalline material: a. has well-defined distances between atoms; b. is not amorphous; c. has long-ranged translational symmetry; all of the above; e. only b and c 13. An amorphous solid: a. is also referred to as a glass; b. is not crystalline; c. does not deform at appreciable rates below its glass-transition temperature, Tg; d. flows under stress at temperatures above T9; @ all of the above. 14. Cement: a) is a polymer; b: forms when water evaporates from a wet mixture of CaO and SiOz—based powders; orms by a chemical reaction between water, CaO powder, and SiOz-based powder; is a good electrical conductor. ‘15. A ceramic made by sintering a cast-and-dried slurry: O‘\ a) is 100% dense; ' b) is easy to machine into its final shape; 0) can be easily melted; is a good electrical conductor because of residual water; @ one of the above. 16. Cement: a) is a polymer; 13) forms when water evaporates from a wet mixture of CaO and SiOg—based powders; c) rms by a chemical reaction between water, CaO powder, and SiOz-based powder; is a good electrical conductor; e) none of the above. ...
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ss_quiz_1 - E—344 Spring 2006 Name; \,\%’;_;§j;p. Quiz...

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