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Engineering Materials

Subject : engineering
Instructions:
  • Answer 50 questions in 15 minutes.
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  • Match each statement with the correct term.
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This is a study tool. The 3 wrong answers for each question are randomly chosen from answers to other questions. So, you might find at times the answers obvious, but you will see it re-enforces your understanding as you take the test each time.
1. Increase temperature - no increase in interatomic separation - no thermal expansion






2. Light Amplification by Stimulated Emission of Radiation






3. Resistance to plastic deformation of cracking in compression - and better wear properties.






4. Energy is stored as atomic vibrations - As temperature increases - the average energy of atomic vibrations increases.






5. Different orientation of cleavage planes in grains.






6. With Increasing temperature - the saturation magnetization diminishes gradually and then abruptly drops to zero at Curie Temperature - Tc.






7. As the applied field (H) increases the magnetic domains change shape and size by movement of domain boundaries.






8. 1. Metals: Thermal energy puts many electrons into a higher energy state. 2. Energy States: Nearby energy states are accessible by thermal fluctuations.






9. 1. Diamagnetic (Xm ~ 10^-5) - small and negative magnetic susceptibilities 2. Paramagnetic (Xm ~ 10^-4) - small and positive magnetic susceptibilities 3. Ferromagnetic - large magnetic susceptibilities 4. Ferrimagnetic (Xm as large as 10^6) - large m






10. Materials change size when temperature is changed






11. A measure of the ease with which a B field can be induced inside a material.






12. Undergo extensive plastic deformation prior to failure.






13. Digitalized data in the form of electrical signals are transferred to and recorded digitally on a magnetic medium (tape or disk) - This transference is accomplished by a recording system that consists of a read/write head - "write" or record data by






14. Width of smallest feature obtainable on Si surface






15. Sigma=ln(li/lo)






16. Is reflected - absorbed - scattered - and/or transmitted: Io=It+Ia+Ir+Is






17. Growing interconnections to connect devices -Low electrical resistance - good adhesion to dielectric insulators.






18. Process by which metal atoms diffuse because of a potential.






19. The magnetic hysteresis phenomenon: Stage 1: Initial (unmagnetized state) Stage 2: Apply H - align domains Stage 3: Remove H - alignment remains => Permanent magnet Stage 4: Coercivity - Hc negative H needed to demagnitize Stage 5: Apply -H - align d






20. They are used to assess properties of ceramics & glasses.






21. Second phase particles with n > glass.






22. Transformer cores require soft magnetic materials - which are easily magnetized and de-magnetized - and have high electrical resistivity - Energy losses in transformers could be minimized if their cores were fabricated such that the easy magnetizatio






23. # of thermally generated electrons = # of holes (broken bonds)






24. Found in 26 metals and hundreds of alloys & compounds - Tc= critical temperature = termperature below which material is superconductive.






25. Loss of image transmission - You get no image - There is no light transmission - and therefore reflects - scatters - or absorbs ALL of it. Both mirrors and carbon black are opaque.






26. Ohms Law: voltage drop = current * resistance






27. Hardness is the resistance of a material to deformation by indentation - Useful in quality control - Hardness can provide a qualitative assessment of strength - Hardness cannot be used to quantitatively infer strength or ductility.






28. Stress concentration at a crack tips






29. Dimples on fracture surface correspond to microcavities that initiate crack formation.






30. Liquid polymer at room T - sandwiched between two sheets of glass - coated with transparent - electrically conductive film. - Character forming letters/ numbers etched on the face - Voltage applied disrupts the orientation of the rod- shaped molecule






31. 1. Tc= critical temperature- if T>Tc not superconducting 2. Jc= critical current density - if J>Jc not superconducting 3. Hc= critical magnetic field - if H > Hc not superconducting






32. The Magnetization of the material - and is essentially the dipole moment per unit volume. It is proportional to the applied field. Xm is the magnetic susceptibility.






33. To build a device - various thin metal or insulating films are grown on top of each other - Evaporation - MBE - Sputtering - CVD (ALD)






34. Increase temperature - increase in interatomic separation - thermal expansion






35. The ability of a material to absorb heat - Quantitatively: The energy required to produce a unit rise in temperature for one mole of a material.






36. A parallel-plate capacitor involves an insulator - or dielectric - between two metal electrodes. The charge density buildup at the capacitor surface is related to the dielectric constant of the material.






37. Created by current through a coil N= total number of turns L= length of turns (m) I= current (ampere) H= applied magnetic field (ampere-turns/m) Bo= magnetic flux density in a vacuum (tesla)






38. Failure under cyclic stress 1. It can cause part failure - even though (sigma)max < (sigma)c 2. Causes ~90% of mechanical engineering failures.






39. 1. Data for Pure Silicon - electrical conductivity increases with T - opposite to metals






40. 1. Insulators: Higher energy states NOT ACCESSIBLE due to gap 2. Semiconductors: Higher energy states separated by a smaller gap.






41. Because of ionic & covalent-type bonding.






42. Allows flow of electrons in one direction only (useful to convert alternating current to direct current) - Result: no net current flow






43. Metals are good conductors since their _______is only partially filled.






44. Occurs at a single pore or other solid by refraction n = 1 for pore (air) n > 1 for the solid - n ~ 1.5 for glass - Scattering effect is maximized by pore/particle size within 400-700 nm range - Reason for Opacity in ceramics - glasses and polymers.






45. High toughness; material resists crack propagation.






46. Heat capacity.....- increases with temperature -for solids it reaches a limiting value of 3R






47. These materials are relatively unaffected by magnetic fields.






48. 1. Ductility- % elongation - % reduction in area - may be of use in metal forming operations (e.g. - stretch forming). This is convenient for mechanical testing - but not very meaningful for most deformation processing. 2. Toughness- Area beneath str






49. Occur due to: restrained thermal expansion/contraction -temperature gradients that lead to differential dimensional changes sigma = Thermal Stress






50. The size of the material changes with a change in temperature - polymers have the largest values







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