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GATE 2015 : Engineering Sciences [Section D]

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GATE 2015 MATERIAL SCIENCE- XE-C C : MATERIALS SCIENCE Q. 1 Q. 9 carry one mark each. Q.1 Arrange the following elements in order of increasing melting point: (P) gallium (Q) tungsten (R) aluminium (S) gold (A) P < R< Q < S (B) S < P < R < Q (C) P < R < S < Q (D) R < S < Q < P Q.2 When the atoms in a solid are separated by their equilibrium distance, A) the potential energy of the solid is lowest B) the force of attraction between the atoms is maximum C) the force of repulsion between the atoms is zero D) the potential energy of the solid is zero Q.3 To which of the following category of materials does Teflon (PTFE) belong? (A) Thermosets Q.4 (B) Thermoplastics (C) Elastomers (D) Block copolymers Which of the following statements is TRUE about the glass transition temperature (Tg)? (A) Tg appears below the melting temperature in a perfectly crystalline material (B) Upon heating through Tg, heat capacity remains constant but the thermal expansion coefficient changes (C) Upon heating through Tg, heat capacity changes but the thermal expansion coefficient remains the same (D) Upon heating through Tg, both the heat capacity and thermal expansion coefficient change Q.5 The slope of a graph of loge(conductivity) versus 1/T (where T is the temperature) for an intrinsic semiconductor with energy gap Eg, is (A) Eg/2k Q.6 (C) Eg/k (D) Eg/k (C) forging (D) tape casting Which is NOT a ceramic forming process? (A) extrusion Q.7 (B) Eg/2k (B) slip casting Which of the following is NOT a soft magnetic material? (A) Iron-silicon steel (B) Nickel zinc ferrite (C) Nickel iron alloy (D) Alnico Q.8 The eutectic reaction is [Note: S solid; L liquid] (A) S1 S2 + S3 (B) L S1 + S2 (C) L1 + S1 L2 + S2 (D) L1 + S1 S2 + S3 XE-C 1/3 GATE 2015 Q.9 MATERIAL SCIENCE- XE-C Vacancies play an important role in (A) deformation twinning (B) self diffusion (C) strain hardening (D) cross-slip Q. 10 Q. 22 carry two marks each. Q.10 Match the techniques listed in Column I with the characteristics of the materials measured in Column II. Column I P. DSC Q. XRD R. STM S. SEM Column II 1. Density of states 2. Glass transition temperature 3. Cathodoluminescence 4. Crystal structure 5. Thermal expansion coefficient (A) P-2, Q-3, R-4, S-1 (B) P-5, Q-4, R-5, S-1 (C) P-2, Q-4, R-1, S-3 (D) P-3, Q-5, R-4, S-2 Q.11 The mass of an electron would increase _____________ times its original mass if it travels at 96% of the speed of light. Q.12 With increasing temperature from 15oC in winter to 45oC in summer, the length of an iron rail track increases by 0.05 cm. Calculate the original length of the iron rail track in cm. (linear thermal expansion coefficient of iron is 11.0 x 10-6 K-1) Q.13 What is the thickness (in m) of a germanium crystal layer that would be required for absorbing 80% of the incident radiation whose wavelength is 1.3 m? The absorption coefficient ( ) of germanium at 1.3 m is 3.3 x 105 m-1. Q.14 A 1 kg sacrificial anode of Mg (atomic weight: 24.31 amu) is attached to the base of a ship. If the anode lasts for 60 days, what is the average corrosion current (in Amperes) during that period? Q.15 A capacitor has a 0.075 cm thick BaTiO3 dielectric with a dielectric constant of 2000 and an electrode area of 0.2 cm2. What is the capacitance of this capacitor in nF? Q.16 A hot pressed ceramic composite material consists of 30 volume % SiC whiskers in an Al2O3 matrix. The measured bulk density of this composite is 3.65 g cm-3. If the theoretical density of SiC is 3.22 g cm-3 and that of Al2O3 is 3.95 g cm-3, estimate the porosity (%) of the composite, assuming that the linear rule of mixtures is valid in this case. XE-C 2/3 GATE 2015 Q.17 MATERIAL SCIENCE- XE-C Match the technical ceramics listed in Column I with their common applications listed in Column II Column I P. Y-doped ZrO2 Q. UO2 R. Si3N4 S. AlN T. Cr doped Al2O3 Column II 1. Lasers 2. Turbine engine 3. Integrated circuit substrate 4. Oxygen sensor 5. Nuclear fuel 6. Thermistor (A) P-6, Q-4, R-5, S-1, T-3 (B) P-4, Q-5, R-2, S-3, T-1 (C) P-3, Q-1, R-2, S-6, T-5 (D) P-1, Q-4, R-5, S-2, T-1 Q.18 Creep in metals is defined as (A) the maximum energy a solid can absorb elastically (B) the maximum energy a solid can absorb by plastic deformation (C) the stress at which plastic deformation starts (D) slow plastic deformation due to diffusion of atoms usually at high temperature (T > half the melting point) Q.19 Calculate the planar density of the (100) plane in an fcc crystal given that R is the atomic radius of the element. (A) 0.25 R2 (B) 0.25/R2 (C) 1/R2 (D) 4/R2 Q.20 The diffusion coefficient of copper atoms in aluminium is found to be 1.28 x 10-22 m2s-1 at T=400K and 5.75 x 10-19 m2s-1 at T=500K. Find the temperature (in Kelvin) at which the value of the diffusion coefficient is 10-16 m2s-1 Q.21 Calculate the density of copper in kg m-3 given that copper has an fcc lattice with a lattice parameter of 0.365 nm. Copper has an atomic weight of 63.54 amu. Q.22 What would be the maximum number of electron-hole pairs that can be generated using a silicon detector irradiated by x-ray of energy 1.54 keV. The band gap of silicon is 1.1 eV. END OF THE QUESTION PAPER XE-C 3/3

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