Could you guys please check to see if the answers for all the multiple-choice questions below are correct? If you find any questions with the wrong answers, please help me choose the correct answers for those questions! Thank you very much!

23. Number of atomic sites per cubic meter for copper is equal to N=8x10", which of the following answers corresponds to number of vacancies at T=1000.C? Activation energy Qa=0.9 ev and gas constant k=8.62x10" eV/K 8. 28628 + 10.9. 7 Date: Tuesday Feb. 18, 2003 Page 6 out of 7 Prof. A. Varvani RE18exp - 2. 2 (a) Ny=1.2x1025 vacancies/m (b) Ny=9.2x1025 vacancies/m (c) Ny=2.2x10" vacancies/m [Equation: Ny=Nexp(-Qa/kT)] (d) Ny=8.0*10" vacancies/m' = (2E28) exp/- 0.9/6 626-8/1237 )(6CCC) EXP(- 0. 9/ 8. 62E-5) (12:75)) 24. The atomic packing factor for given HCP unit-cell is APF=0.75. If the volume of (a) 0.1026nm HCP unit-cell is V=0.08 nm', determine the radius of atoms of this unit-cell. : (b) 0.1510nm 6ators / cell +c (c) 0.1336nm +a3 (d) 0.1210nm APF = R - Za . 75 - 6(a) -08 Fa2 +al 25. The energy in Jules (J) of a photon whose wavelength is 2=121.6 nm (h=6.63x10 34J.sec and C=3E8 m/sec. & AE=hC/2). (a) 1.02x10-20 J (b) 1.63x10-18 J ( 6 . 6 3 6 - 34 ) ( 5# 8 ) (c) 2.12x10-19 J (d) 1.99x10-19 J 121. 6 26. Which one of the following crystallographic planes represents FCC and BCC planes, respectively? (1) (2) (3) (4j V2 (a) 1: BCC, 2: BCC, 3: FCC, 4: FCC (b) 1: FCC, 2: BCC, 3: Fee, 4: BCC (c) 1: BCC, 2: FCC, 3: FCC, 4: BCC (d))1: BCC, 2: FCC, 3: BCC, 4: FCC 27. The length of the Burger's vector (b) in a BCC Lithium (with a=0.351nm) along the close-packed direction of is: (a) 0.501 nm (b) 0.304 nm (c) 0.152 nm (d) 0.251 nm28. Identify the element having an inter-planar spacing of dio=0.2237 nm, and (a/R)=2.828 (use: dnki=a/(h2+k2+12) 0.5) a (a) Manganese with atomic radius of 0.112 nm. ads. 2237 = (b) Nickel with atomic radius of 0.125 nm. (c) Cadmium with atomic radius of 0.197 nm. (d) Tungsten with atomic radius of 0.137 nm. 29. The time it required to obtain a carbon concentration of Cx=0.30 at a depth of x=0.005-m beneath the surface of an iron bar when carburizing at 1273 K is: where: Co=0.20, Cs=0.45 and D=2.979x10-"! (. 95 - -3) . 005 (c, -C.)/(c, -co)=erfx 2NDI ( .45-.2) Use the Fick's second law and error function table given: . /240 = 20 Z 0.50 0.55 0.60 0.65 0.70 0.75 erf (z) 0.5205 0.5633 0.6039 0.6420 0.6778 0.7112 212.959E-11 + 6 = of (a) t=612 mins 2 57600 = ent2 (b) t=3492 mins 4(2.2879 6-1/- ) (c) t=13806 mins (d) t=9870 mins er - 2. 36- 3t 30. If the number of diffusing Ni atoms crossing a 2cmx2cm interface plane is 1.54x1013 Ni atoms/cm .sec. Which one of the following answers does correspond to the number of Ni atoms/sec. Passing through this plane? (a) 7.11x10' Ni atoms/sec. (b) 1.20*1010 Ni atoms/sec. (c) 8.20x108 Ni atoms/sec. (d) 6.16*10" Ni atoms/sec