test3s202

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Home Introduction Policies Resources Requirements & Grading Syllabus Assignments Handouts Discussion Web Links Distance Learners Contact MSE 200 Test 3

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Formulae: σ = σ o exp(-t/t r ), t r = t ro exp(Q/kT), K IC = σ f( π c) 1/2 , e'= e o 'exp(-Q/kT), x=(Dt) 1/2 , η = η o . exp(Q/kT), σ = σ o exp(-Eg/2kT), σ = σ o exp(-Ed/kT). Q1 The viscosity of a glassy material has decrease by a factor of 2 when the temperature is increased from 150 o C to 200 o C. It is desired to know viscosity when the temperature is at 100 o C compared to its value at 150 o C. 1. The activation energy for viscous flow is a. 5252.2 k b. 2774.8 k c. 1252.4 ( b ) 2. Value of viscosity at 100 o C compared to that at 150 o C is a. 2.44 b. 0.82 c. 0.41 ( a) Q2. A polyethylene sample was subjected at room temperature to a tensile stress of 50 Psi and the stress is reduced to 25 Psi after 5 minutes when the cross-heads are held without movement. It is desired to what will be the load after 30 minutes. 1. The relaxation time of the polymer is a. 7.21 minutes b. 2.0 minutes c. 5.0 minutes ( a ) 2. The load after 30 minutes is a. 72.2 Psi b. 3.2 Psi c. 1.6 Psi ( c ) Q3. Molecular weight of Na 2 O is 62 and that of SiO 2 is 60. If 120 gms of SiO 2 and 31 gms of Na 2 O are mixed and heated together and cooled rapidly can we get glassy phase. 1. The number of molecules of SiO 2 and Na 2 O present in the mixture are: a. Na 2 O............................ 2.0 ( b ) b. SiO 2 ............................. 0.5 ( a ) 2. The Oxygen :Silicon ratio in the mixture is a. 4 b. 3 c. 2.25 ( c ) 3. Is it possible to form a glassy phase by cooling above the cooling rate a. yes b. no c. not sure ( a ) Q4. The energy of the donor level compared to the minimum of the conduction band edge in silicon is 1464.4 k where k is the Boltzmann's constant. The band gap of silicon is 12790.7 k . If the temperature is increased from room temperature (27 o C) to 77 o C, calculate the factor by which the donor induced conductivity increases. Calculate the factor by which the intrinsic carrier induced conductivity increases for the same temperature change. 1. The factor by which the donor induced current increases compared to the
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