finalspr01

# finalspr01 - ~ \ FINAL ENSC 3313, Spring 2001 Answer any 20...

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~ \ ENSC 3313, Spring 2001 FINAL Name Answer any 20 Questions only, 2 points each. At the British Nuclear Fuels (BNF) reprocessing center, they are discharging small amounts of radioactive technetium into the North Sea. The half life of Tc:~ is 2 x 105y, so what proportion ~ in 500y? (New Scientist, March 2001). The decay is exponential with time. At -t/A -2/A in units of 105 A = 2.89 y 0.5 = e ~=e Ao Would radiation of wavelength 5.000 ~m cause promotion of electrons in a semiconductor of band gap 1.3 eV? The velocity of light is 3.0 x 108 mls; h = 6.62 x 10-33 Js; F = 96.5 x 103C; 1 eV = 1.6 x 10-19 J. 2. hc A AB= The equation is ~ .62X10-3 3x108 1.9< 5.0x10-6 1.6x10-19 hc A We need AB< 1.9 < 2.48 ". hence, Sketch 4 two- fold axes of symmetry in the tetragonal cell shown (a= b * c; a = 13 = y = 900). 3 Put axes through the middle of the two pairs of opposite rectangular faces and through the two pairs of opposite side edges of these faces.

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~...~I/t Sf Identify the lattice plane and lattice direction sketched. 4 For ~, we need the reciprocals of fractional intercepts along the axes. y O 1/4 With origin at '0', we get intercepts of -{1/4), {1), {00), hence plane is (410 ). x For direction, we go from start to end of line in cell, hence --(1/4) (1), (-1). Clearing fractions, [144] Direction lies in plane, --hu + kv + £w = 0. ~ (4xl)+(lx4)+(Ox4)= 0 Sodium is a Group I BCC metal of atomic radius 0.186 nm. The charge on an electron is 1.6 x 10-19C; the electron mobility (~) in sodium is 0.0053 m2Ns. What is the likely electrical conductivity of sodium, .Q.-lm-l? (Calculate number of atoms/m3 first.) 5 For a BCC metal, atoms contact along the cube diagonal, 4R.J3 a Hence 'a' = 4(0.186)/.J3 = 0.4295 nm . We will equate 1 atom to 1 charge carrier. We have 2 atoms/cell, so 2 charge carriers per a3 per 0.079 nm3. Hence, per m3 we have {f' r\,. .,r\ i1 r\-27 \ -2.52x 1028 /m3. \0.079 J\xI0- J 0" = nq~ = (2.52) (1028) (1.6) (10-19) (0.0053) 0" -2.13 x 108 o.-lm-1 6. The micrograph below shows the crystal grains in a metal at 100x. Please determine the ASTM grain size number. T count -64 grains per in2 ~, ~, -,-,' .I'-'" .l 1 m -' "'- 1" ~"". ,'. ., ..r.' .~' ~ ~' 1 If I "ty ( ~ ,Q;- ..- ~ ~<l .kJ' 1).{ -l.,K , :tJ The magnification is 100x, so no adjustment needed. N = 2n-l = 64 = 26 6=n-l n=7 h-JY\r;~ .i-. .;. v ~ \.-'--t1
7. D = Doe-Q/RT -T;) -Q ( 1 -R"m ( D ) I I In = -6128 - l.OSxlO-14 ( ) 298 1 273 D = 6.90 x 10-14 cm2/s The value falls between the 50° and o°C values, so is reasonable. 8 A .flm tensile test specimen of gauge length 4 inches and width 1.0 inches was cut from sheet 0.2 inches thick. The ~ elQngation plot is as shown. Calculate the a) elastic modulus, b) yield strength, c) tensile strength, d) % elongation (4"). The width = 1 ", the thickness = 0.2".

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## This note was uploaded on 01/10/2012 for the course ENSC 3313 taught by Professor Staff during the Fall '11 term at Oklahoma State.

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finalspr01 - ~ \ FINAL ENSC 3313, Spring 2001 Answer any 20...

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